In a small bowl, combine the flour, chile powder, salt and pepper. Dust the fillets on both sides with the flour mixture.
Heat the oil and butter in a large skillet over medium-high heat. Put the fillets in the pan and cook for 4 to 5 minutes, then flip and cook for an additional 4 to 5 minutes, or until the fish flakes when you poke it with a fork. Remove to drain on a paper towel. Transfer the fillets to a serving plate and break each into a few big pieces.
Divide the fish evenly among the tortillas and top with the Citrus Salsa.
To Make Citrus Salsa: In a glass bowl, mix all the ingredients together. Cover and refrigerate for 1 hour. Mix again before serving. Makes 2 cups.