Lightly spray grill rack with nonstick cooking spray, and preheat grill.
Sprinkle both sides of fish with fajita seasoning, gently pressing into flesh. Grill fish 3-4 minutes on each side or until fish flakes easily when tested with a fork. Flake into pieces with a fork; keep warm.
In a small bowl, mix together cabbage, lime juice, salt, and cilantro.
Wrap the tortillas in paper towels, and microwave 1 minute on HIGH or until they’re warm.
Place taco ingredients on the table for assembly. Spread each tortilla with 1 teaspoon of sour cream, if desired, and top with fish, cabbage mixture, and avocado. Serve with salsa and lime wedges on the side.