n a small saucepan, melt butter over medium low heat. Whisk in flour and salt to make a paste. Gradually whisk in milk. Stirring constantly, cook until sauce is thick enough to coat the back of a spoon.
Select a pan large enough to accommodate all the fillets in one layer. Coat with cooking spray. Arrange fish in pan, and cover with shrimp.. Pour white sauce over shrimp. Sprinkle with grated cheese.
Bake, uncovered, for 20 to 25 minutes.
3 tablespoons butter
2 tablespoons all-purpose flour
1/2 teaspoon salt
1 cup milk
2 pounds red snapper fillets
1/2 pound cooked medium shrimp, peeled and deveined
1/4 cup grated Parmesan cheese