Baked Salmon with spinach and mushrooms

4 salmon fillets (1 lb.)
2 cups chopped fresh spinach leaves
1 cup sliced mushrooms
1 tomato, chopped
1/3 cup Sun-Dried Tomato Dressing

HEAT oven to 375°F. Place fish fillets, skin sides down, in 13x9-inch baking dish sprayed with cooking spray.
MIX remaining ingredients until blended; spoon over fish.
BAKE 20 to 25 min. or until fish flakes easily with fork.