Preheat an indoor or outdoor grill to medium-high heat.
Pat the fish dry and drizzle lightly with olive oil.
Combine chili powder, cumin, paprika, cayenne, salt, and black pepper. Rub the seasoning evenly over both sides of the fish.
Grill the Grilled Mahi Mahi Fish Tacos fish for about 5–6 minutes per side, depending on thickness, until the fish flakes easily and develops a lightly charred crust.
Remove from the grill and squeeze fresh lime juice over the fish.
In a bowl, combine cabbage, cilantro, red onion, and lime juice. Toss until evenly coated.
Warm the corn tortillas.
Assemble each taco by adding slaw, large flakes of grilled fish, pico de gallo, sliced avocado, and a drizzle of avocado tomatillo salsa.
Serve immediately with extra lime wedges.