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 at least 6 hours, giving time for the flavors to blend.
Serve with chopped cilantro and slices of avocado with heated tortillas for
ceviche tacos or with tortilla chips.