1. In a large skillet cook ground beef, onion, and garlic until meat is browned; drain off fat. Stir in spaghetti sauce, stewed tomatoes, and mushrooms. Bring to boiling; reduce heat. Cover and simmer 10 minutes.
2. Meanwhile, cook pasta according to package directions; drain. In a 2-quart casserole or a 4-quart Dutch oven layer half each of the pasta, the meat sauce, sour cream, and cheese. Repeat layers. Bake, uncovered, in a 350 degree F oven for 25 to 30 minutes or until heated through. Garnish with shredded lettuce, if desired. Makes 6 servings.