1 can (4 ounces) sliced mushrooms
Drain mushroom liquid into a measuring cup; add water to make 1 cup liquid. Add to the milk. Melt 2 tablespoons of butter or margarine in a large saucepan; blend in flour, salt and pepper. Stir over low heat until smooth; gradually stir in milk mixture and continue stirring and cooking over low heat until thickened. Add tuna, mushrooms and spaghetti; transfer to a 1 1/2-quart casserole; sprinkle with Parmesan cheese. Melt remaining 2 tablespoons of butter or margarine; toss with bread cubes. Arrange bread cubes over top of casserole. Bake casserole, uncovered, at 350° for about 25 to 30 minutes.