To prepare crema, combine the first 8 ingredients in a small bowl; set aside.
To prepare tacos, combine cumin and next 5 ingredients (through garlic powder) in a small bowl; sprinkle spice mixture evenly over both sides of fish. Place fish on a baking sheet coated with cooking spray. Bake at 425° for 9 minutes or until fish flakes easily when tested with a fork or until desired degree of doneness. Place fish in a bowl; break into pieces with a fork.
Heat tortillas according to package directions. Divide fish evenly among tortillas; top each with 1/4 cup cabbage and 1 tablespoon crema.