Preheat oven to 400°F and line a baking sheet with parchment paper.
Pat the fish dry and brush both sides with olive oil.
Mix chili powder, garlic powder, paprika, salt, and black pepper in a small bowl, then sprinkle evenly over both sides of the fish.
Bake fish for 12–15 minutes or until it flakes easily with a fork.
While the fish bakes, add green cabbage, purple cabbage, mayonnaise, lime juice, and sugar to a big bowl. Toss everything until the cabbage is coated.
Warm the tortillas in a dry skillet or microwave until soft.
Break the cooked fish into big pieces with a fork.
Fill each tortilla with fish and a scoop of cabbage slaw. Top with avocado, cilantro, and an extra squeeze of lime if you want.