Cut fillets into serving size portions.
Place fish in a shallow baking dish. Combine dressing, lemon juice and salt.
Pour sauce over fish and let stand for 30 minutes turning twice.
Remove fish from sauce and place in a well-greased baking dish 12x8x2 inches.
Bake in a moderate over, 350 degree for 15 to 20 minutes or until fish flakes easily when tested with a fork.
Crush onions. Add cheese and mix thoroughly.
Sprinkle onion mixture over fish. Bake 5 more minutes to brown onions.