Add the mushrooms, the cooked shrimp (reserve a handful for the top) and stir to blend. Remove from heat. Spread the spaghetti in a large, shallow greased pan. Spoon the shrimp mixture over the spaghetti and top heavily with the parmesan cheese. Garnish the top with the reserved shrimp. Bake in a moderate oven (350 degrees F.) for 20 to 30 minutes or until top is nice and brown. Serve with toasty garlic bread.
Note: The last time I checked for B&B Mushrooms, I could not find them. Here is how I made mine: Melt 3 tablespoons butter in a skillet and add 8 ounces of fresh sliced mushrooms. Saute until brown.