In a non-reactive casserole dish, either pyrex or ceramic, place the fish, onion, tomatoes, chilli, 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 flavours to blend.
For the slaw, slice the white cabbage into thin strips, along with the red onion, mix the rest of the ingredients together in a bowl.
Place two tacos side by side and load up with filling.