Preheat oven to 350 degrees. Prepare large baking pan with vegetable pan-coating. Cut fish into 6 serving pieces. Arrange onion in bottom of baking pan. Place fish on top of onion. Combine remaining ingredients except margarine and lemon wedges. Spread on top of fish. Dot with margarine. Bake 25-30 minutes or until fish flakes easily with a fork. Serve with lemon wedges.