In a large bowl, combine the flour, chili powder, salt, pepper and garlic powder. Add tilapia fillets, one at a time, and turn to coat.
In a large nonstick skillet over medium heat, cook fillets in butter for 5-6 minutes on each side or until fish flakes easily with a fork. Meanwhile, place tortillas on a baking sheet and spritz with cooking spray. Broil 3-4 in. from the heat for 2-3 minutes on each side or until crisp.
In a small bowl, toss the coleslaw mix, mayonnaise, sour cream, lime juice and zest. Cut fish into large pieces. On each tortilla, layer coleslaw, black beans, fish and avocado.