Wash fish and dry thoroughly.
Cut foil in approximately 14-inch squares and place one fish fillet in center of each.
Arrange shrimp and mushrooms over fillets.
Sprinkle with salt, pepper, paprika, and lemon juice.
Top each with about 1/4 cup White Sauce; sprinkle with parsley.
Fasten sides of foil together with double fold to make a tight seal.
Fold in ends of foil.
Recipe may be prepared to this point and refrigerated.
Bake in 400° oven for 35 minutes.
Serve in foil or place in au gratin dishes, if desired.