This Southwestern Casserole is an amazing vegetarian comfort food. It’s layered with grilled zucchini, mushrooms, black beans, caramelized onions, and Latin flavors throughout.
Zucchini is one of the most versatile squashes, and it's incredibly delicious in so many recipes -- from fresh salads and stir-fries, to quick breads and chocolate cakes.
We see it sliced, grated, chopped, grilled, roasted, sautéed, and so on.
Along with a handful of other fresh ingredients, it's one of the stars of this delicious Southwestern Casserole.
Ingredients in Vegetarian Southwestern Casserole
- zucchini
- mushrooms
- black beans
- onion
- garlic
- jalapeño
- chipotles in adobo sauce
- cumin
- cheddar cheese
- pepper jack cheese
- cilantro
- avocado
- olive oil, salt, pepper
This is one very hearty vegetarian casserole, with a spicy Latin flavor profile. I think you’ll love it!
How to Make this Southwestern Casserole
- Slice zucchini thinly, lengthwise, about ¼ inch thick. (The easiest way to do this is to use a mandoline. If you don’t have one, use a Chef’s knife.) 
- Coat the zucchini slices with olive oil and season them generously with salt and pepper. Add them to a very hot grill and cook until they're tender and nicely browned, about 2 minutes per side.
- In a small bowl, combine jalapeño, garlic, chipotles in adobo sauce and cumin. (It's this, the beans and garnishes that really give this Southwestern Casserole its Latin vibe.)
- Add the onion to a large sauté pan lightly coated with oil over medium heat. Cook until soft and golden, about 20 minutes. Then add the seasoning mixture, stir, and cook until aromatic, about 30 seconds. 
- Turn the heat up and add half of the mushrooms. Stirring often, sauté until they’ve shrunk and softened, and then add the rest, and continue to cook until they're golden, about 10 minutes. Mix in the beans and season to taste with salt and pepper.
- Assemble all of the prepared ingredients into a 9 x 13 x 2 inch baking dish as follows: ⅓ of the onion-mushroom mixture, grilled zucchini, ½ cup of the Cheddar and ¼ cup of the Pepper Jack cheese. Repeat this layering process twice more — however, the top layer of cheese will be ¾ cup of the Cheddar and ½ cup of the Pepper Jack.
- Place the baking dish in a preheated 375°F oven and bake for 20 minutes. Remove from the oven, cool a bit, and then garnish with cilantro, avocado and jalapeño slices.
(More detailed instructions are in the recipe card below.)
Recipe Tips and Substitutions
- You can purchase pre-sliced mushrooms. (When they are pre-sliced you still need to wash them!)
- Feel free to use yellow zucchini if you see it, and a combination of yellow and green would be pretty.
- Grilling the zucchini adds a lot of the smoky flavor to this recipe. You can however, sauté the zucchini in a cast iron skillet and it will acquire a lovely caramelization which also adds delicious flavor.
- Avocado, cilantro and jalapeño slices are added to the top of the Southwestern Casserole for the garnish. It brightens up the whole dish and adds great fresh flavor. To save time, you can serve them on the side.
- For more heat in this recipe, do not remove all (or any) of the jalapeño seeds.
Can you make it ahead?
Yes! There are a couple options:
- You can grill the zucchini and sauté the vegetables up to one day ahead. About an hour before serving, assemble, bake and cool.
- Take it one step further and assemble the casserole a day ahead of time. The next day, about 45 minutes before you want to serve, bake it.
Can you freeze it?
Yes! Let it cool completely before freezing. It works very well to cut the casserole into portions, and then freeze them separately. This way, you can grab just enough for one or two, if you’d like.
Be sure it’s wrapped very tightly to avoid air getting in. It can be frozen for up to three weeks. (I wouldn’t recommend freezing the whole casserole, but it’s great for leftovers.)
I hope you love this Vegetarian Southwestern Casserole as much as my family and I do!
More delicious vegetarian casseroles:
- Smashed Potato Casserole
- Lasagna with Swiss Chard
- Vegetarian Potato Moussaka
- Hatch Chile Cornbread Casserole
Vegetarian Southwestern Casserole
Equipment
Ingredients
- 3 pounds zucchini, washed and dried
- olive oil for the pan and coating the zucchini
- 3 cups thinly sliced yellow onion
- 6 tablespoons finely chopped jalapeño pepper, washed and dried, seeds removed,
- 1 tablespoon minced garlic
- 1 tablespoon finely chopped chipotles in adobo sauce,
- 2 teaspoons ground cumin
- 2 pounds (about 10 cups) Button or Crimini mushrooms, washed and dried, thinly sliced
- 1¾ cup cooked black beans, (from scratch or a can -- drain if from a can)
- 1¾ cup Cheddar cheese (white or orange), grated, divided
- 1 cup Pepper Jack cheese, grated, divided
- salt and freshly ground black pepper
Garnishes
- about 1 cup loosely packed cilantro leaves, washed and dried
- about ½ large avocado, thinly sliced
- about 2 tablespoons thinly sliced jalapeño pepper, washed and dried
Instructions
- Prepare the zucchini: Slice about ½ inch off the ends off of the zucchini and then slice them thinly, about ¼ inch. The easiest way to do this is to use a mandoline. (If you don’t have one, use a Chef’s knife. First cut a base by slicing off a thin strip from one side. Then with the zucchini sitting steady of this base, cut it into thin slices.)
- Grill the zucchini: Preheat a stove-top grill (or outdoor grill). On a baking sheet, coat the zucchini slices with olive oil and season them generously with salt and pepper. Once the grill is hot, add the zucchini slices — there should be about an inch between them. Grill until they're tender and nicely browned, about 2 minutes per side. Set aside on a baking sheet to cool.
- Preheat the oven to 375°F.
- Prepare the seasonings: In a small bowl, combine the jalapeño, garlic, chipotles in adobo sauce, and cumin. Set aside.
- Sauté the vegetables: Coat a large sauté pan with olive oil and place it over medium heat. Add the onion and, stirring often, cook until soft and golden, about 20 minutes. Add the seasoning mixture, stir, and cook until aromatic, about 30 seconds. Turn the heat to medium-high, drizzle with a bit more olive oil and add about half of the mushrooms. Stirring often, sauté until they’ve shrunk and softened, about 5 minutes. Add the second half of the mushrooms and continue to sauté until all of the mushrooms begin to brown, about 10 minutes. Mix in the beans and season to taste with salt and pepper. (Here’s How to Season to Taste.)
- Assemble: Add an even layer of the grilled zucchini slices to the bottom of a 9 x 13 x 2 inch baking dish. Cover this with an even layer of about ⅓ of the mushroom-bean mixture. Sprinkle with ½ cup of the Cheddar and ¼ cup of the Pepper Jack cheese. Repeat this layering process twice more — however, the top layer of cheese will be ¾ cup of the Cheddar and ½ cup of the Pepper Jack.
- Bake: Place the baking dish on a sheet pan and place in the preheated 375°F oven. Bake for 20 minutes. Remove from the oven and let it sit for about 15 minutes.
- Garnish: After the 15 minutes of cooling time, garnish with the cilantro, avocado and jalapeño slices.
- Serve!
Notes
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Marissa
Everything about this grilled zucchini casserole is calling my name, Valentina! So many fresh and comforting flavors in one satisfying dish!
valentina
Thank you, Marissa. Enjoy! 🙂 ~Valentina
Eha Carr
As in Australia we are blessed with beautiful zucchini the year around and it happens to be one of my very favourite vegetables, my crisper is guaranteed to always have some waiting for inspiration. Your recipe is naturally interesting with its Tex-Mex suggestions more uncommon here. Eat avocadoes almost every day also . . . but shall have to pick another cheese. Personally I do not buy sliced mushrooms as, at least here, they tend to be not as fresh or of the top quality . . . I also never ever wash them . . . we are all different , , , Thanks !
valentina
Thank you, Eha. I eat avocados every day too. During the summer, at least. 🙂 I can't get enough and seem to add them to almost everything lately. Enjoy! 🙂 ~Valentina
angiesrecipes
This is a GREAT recipe when the zucchini in season and so much better and healthier than lasagna .-))
valentina
Thanks, Angie. Yes, that's exactly what I attempting her -- a healthy and hearty lasagna of sorts. Enjoy! 🙂 ~Valentina
Ron
We love zucchini although we don’t see local grown that often. I guess they don’t like our climate. Ours mostly come from Italy and Spain.
Great recipe idea, it has me thinking of veg nachos without the chip.
valentina
Ron, I love that comparison of the nachos!! Thank you. Hope all is well in your part of the world -- it's better than it is here for sure. Hoping California takes a turn for the better soon. In the meantime, I'll just keep cooking. 🙂 ~Valentina
David @ Spiced
We have a ton of zucchini in the fridge right now - what a delicious way to use 'em up. Plus, grilled zucchini is delicious! 🙂
valentina
Enjoy, David. Thanks so much for checking out the recipe. 🙂 ~Valentina
Dawn- Girl Heart Food
What a fabulous comfort food meal! Love that zucchini is the star of the show. Would love a piece for supper tonight!!
valentina
Thank you, Dawn. Enjoy and hope all is well! 🙂 ~Valentina
Priya
Grilled zucchini sounds really delicious. This casserole recipe is going to be our favorite for sure.
valentina
Thanks so much, Priya. Hope you love it! 🙂 ~Valentina
David Scott Allen
I think I have everything on the list except the avocado and jalapeno - so I think I can live without those. We are buying a lot of squash at the market these days - this week it was all yellow squash. And I bought three bags of mushrooms (sliced) at Trader Joe's - it is as if I knew you were going to post this. Oh, and I will have to switch out something for the jack cheese - I have cheddar and Gouda. I am sure we will suffer that switch well. Will report back! The nice thing about this Dinner one night, and a couple of lunches to follow! (Leftovers for dinner in our house is verboten... by me! 🙂
valentina
Oh I hope you love it, David! Thanks so much. The alterations you're making sound delicious! Enjoy and hope you and Mark are doing well. 🙂 ~Valentina
David Scott Allen
It is in the oven with 4 minutes to go! It smells fantastic. For the mozzarella, w used a third each of mozzarella, Gouda, and La Vache Qui Rit. (Yes, I had that...) half the mushrooms, zucchini, and onions in am 8x8 pan. Yum!
David Scott Allen
O. M. G. — this is fabulous! Having seconds now.
valentina
David, this makes me so happy!!! Thank you so much for sharing. 🙂 ~Valentina xo
Kim Lange
I love this recipe so much! I cannot wait to make it! My neighbor brought me some zucchini and this looks super amazing! TASTY & Pinning! 🙂 Thanks for sharing.
valentina
Thanks, Kim. Luck you to have a neighbor who bring you fresh produce. Enjoy! 🙂 ~Valentina
2pots2cook
Beautiful vegetarian lasagna idea !!!! Absolutely keeper in our house 🙂
valentina
Thanks, Davorka. Hope you and your family love it. Stay well! 🙂 ~Valentina
Kathy @ Beyond the Chicken Coop
What a great dish and a great way to use up that garden zucchini! I love that you can make this now and freeze for later. Makes great sense to use while we have all this great zucchini!
valentina
Thanks, Kathy. Hope you love it! 🙂 ~Valentina
Gerlinde
One can never have too many recipes for zucchini. I am growing my own zucchini this year and I can try your recipe with them. Thanks!
valentina
So lovely to be growing your own food. I love it. Thank you and enjoy! 🙂 ~Valentina
Liz
Oh, my, I love everything about this yummy casserole! Since the picky husband won't eat zucchini OR mushrooms, it would be MY lunch all week long. I can't wait to give it a try.
valentina
Thanks so much, Liz. Hope you enjoy! 🙂 ~Valentina
John / Kitchen Riffs
Love zucchini! In fact we're having it in a stir-fry tonight. Might have to rethink that plan and make this instead -- what a wonderful dish. I make something vaguely similar (kinda sorta the same concept, but the flavors are totally different), but really like how you've put together this recipe. Thanks.
valentina
Thanks so much, John. Hope you enjoy it -- or any variation of it. 🙂 ~Valentina
Colette
Gorgeous! I'm always oozing for meatless, but tempting dishes abd this one's on the docket for Monday night! xo
valentina
Hi Colette! Hope you and your family love it. 🙂 ~Valentina
Kim Lange
Looks super amazing Valentina!! Pinning to make later!
valentina
Thanks for checking them out, Kim. And for the pin. 🙂 ~Valentina
2pots2cook
Such a beautiful dish. Printing out to keep!
valentina
Yay. Hope you love it, Davorka. Thank you. 🙂 ~Valentina