In a medium bowl, combine flours and taco seasoning of choice. (I prefer blackened fish seasoning for these, but taco seasoning is another option.)
Cut thawed fish into small pieces (kitchen scissors work great for this). Pat fish pieces dry with paper towels. Heat large cast-iron skillet on medium-high.
When cast-iron skillet is hot, add about 2 to 3 tablespoons of avocado oil (or olive oil if heat is on low-medium). Dredge each piece of fish into the flour seasoning mixture thoroughly. Place fish pieces into hot pan, careful not to crowd.
Options for cooking:
Option 1: Partially cook each fish piece for 1 to 2 minutes on each side, carefully turning only once with a sturdy spatula, just to brown and crisp the outside. Place on foil-lined sheet pan. (I like this method because you can pause here to prep the fish ahead of time; refrigerate pan if needed, and then continue later when ready to eat.) Finish cooking in 375-degree oven for approximately 10 minutes (time may vary depending on size of fish pieces) while you prepare toppings of choice.
Option 2: Cook for 3 to 4 minutes on each side, carefully turning only once with a sturdy spatula, or until cooked thoroughly in center of each piece of fish (cooking time will depend on thickness of fish pieces).