In a medium bowl, combine the cabbage, avocado, mango, onion, cilantro, lime juice, and salt and pepper to taste. Set aside at room temperature.
In a large nonstick skillet over medium-high heat, heat the oil. Season the fillets lightly with salt and pepper and cook for 3 minutes on each side, or until the fish flakes easily. (The cooking time will depend on the thickness of the fish.)
Divide the fish and cabbage salad among the tortillas and serve with lime wedges.