HEAT oven to 350ºF. Place fish in single layer in shallow baking dish. Bake 25 min. or until fish flakes easily with fork. Flake fish; place in medium bowl. Stir in 1 cup cheese, sour cream, dressing, onions, 1/4 cup olives, chilies and seasoning mix. Spoon down centers of tortillas; roll up.
POUR 1/2 the enchilada sauce onto bottom of 13x9-inch pan. Top with enchiladas, seam-sides down. Cover with remaining sauce and cheese.
BAKE 25 to 35 min. or until heated through. Top with lettuce, tomatoes and remaining olives.