Preheat oven to 350 degrees.
Cook spaghetti according to package directions, drain when el dente.
In a Dutch oven saute the onions and garlic in butter until tender, add the mushrooms and saute for 3 minutes..
Stir in the soup, turkey, broth, sherry, Italian seasoning, salt and pepper and 1 cup of cheese.
Toss the pasta into turkey mixture.
Transfer to two greased 8 in square baking dishes or one 9×13 dish.
Sprinkle with remaining cheese.
Bake for 30-40 minutes or until heated through.
Cover and freeze the other casserole for up to 3 months.