Mix the lime and orange juice in a medium-sized glass bowl. Add the shrimp, cover with plastic wrap, and let it marinate for at least 4 hours in the refrigerator.
Remove the marinating shrimp from the refrigerator and gently mix in the tomatillo, tomato, onion, pepper and cilantro, cover and return to the refrigerator to marinate for about 1 more hour, or until the shrimp appears to be "cooked." It should be completely opaque and slightly pink.
Drizzle with a bit of extra virgin olive oil and season generously to taste with salt and pepper.
Notes
You can adjust the amount of Serrano pepper you add, depending on how much heat you like. The amount listed in the recipe makes the ceviche medium hot.Are you wondering how the shrimp in the ceviche is "cooked?" Wonder no more! The acid from the citrus actually changes the structure of the proteins in the seafood, essentially "cooking" it without using heat.