Place the potatoes (leaving them whole with the skin on!), in a large pot of water and bring to a boil. Reduce the heat and simmer just until the potatoes are tender enough to get a fork in easily, about 20 minutes. They should not be so tender that they fall off of the fork, as you want them slightly undercooked at this point.
Drain the potatoes and let them cool them enough to hold them. While they are still warm, use your hands to remove the skin -- it should come right off. Set aside.
Preheat the oven to 375 degrees F.
Coat the bottom of a large sauté pan with olive oil, and place it over medium heat. Add the onion and garlic, and stirring occasionally, cook until the onions are beginning to brown, about 10 minutes.
Add the chipotles, cumin, and dried and fresh oregano. Let this cook until it's very aromatic, about 2 minutes. NOTE: If don't want too much heat in this dish, remove some or all of the chipotle seeds. Also, I like to use just the adobo sauce for 2 of the 5 tablespoons.)
Add the tomato and stir to blend. Turn the heat to low and let the sauce simmer, uncovered, until it thickens a bit, about 20 minutes.
Mix in the agave and scallions, and season to taste with salt and pepper.
Now you can cut the potatoes. Slice them into approximately ⅛ to ¼-inch discs.