Cook spaghetti following package directions; drain. Place the drained spaghetti, turkey, pimiento, green pepper, and onion in a lightly greased 1 1/2-quart casserole. Pour in cream of mushroom soup and broth or water; add salt, pepper, and 1 1/4 cups of the cheese. Lightly toss to blend ingredients; top with remaining cheese. Chill casserole. About 1 hour before serving time, heat oven to 350°. Bake turkey spaghetti casserole for about 45 minutes, or until hot and bubbly.