Place snapper, onion and lime juice in a glass or ceramic bowl; mix and cover. Make sure fish floats freely in lime juice to allow thorough and even marinating. Place in refrigerator and marinate for 1 hour and 45 minutes. Fish is “cooked” when it is white (no longer translucent) and feels firmer to the touch. Remove from refrigerator, strain and set aside. Discard the lime juice.
In a separate bowl, combine tomatoes, jalapeños, cilantro, olives and the olive oil and mix well.
When ready to serve, combine fish with tomato-avocado mixture, add avocado, season to taste with salt and pepper and stir to incorporate.
Serving suggestion: Consider serving ion a martini glass, garnished with avocado slices and cilantro sprigs. Serve each portion at room temperature with totopos on the side.
Notes: This basic ceviche recipe can be varied by using salmon, grouper, shrimp (marinate for 4 hours), tilapia and halibut.
When marinating fish, use your own judgment. If you feel you would like to “cook” the seafood in lime juice for a longer period of time, it is fine. Also, red jalapeños or serranos can be substituted for the green jalapeños.