In a non-reactive casserole dish, either Pyrex or ceramic, place the fish, onion, tomatoes, chili, salt, Tabasco, and oregano. Cover with lime and lemon juice. Let sit covered in the refrigerator for an hour, then stir, making sure more of the fish gets exposed to the acidic lime and lemon juices. Let sit for several hours, giving time for the flavors to blend.

During the marinating process the fish will change from pinkish grey and translucent, to whiter in color and opaque.

Serve with chopped cilantro and slices of avocado with heated tortillas for ceviche tacos or with tortilla chips.