Preheat oven to 450°. Cook ground round and sausage in a large skillet over medium-high heat, stirring often, 8 to 10 minutes or until meat crumbles and is no longer pink. Drain beef mixture, reserving 1 tsp. drippings in skillet. Reduce heat to medium.
Sauté onion in hot drippings 2 minutes. Add garlic, and cook 1 minute or until tender. Add mushrooms, and sauté 8 to 10 minutes or until most of liquid has evaporated. Stir in beef mixture, pasta sauce, Italian seasoning, and salt. Bring to a light boil, and simmer 5 minutes.
Pour beef mixture into baking dish, and sprinkle with cheese. Place entire piecrust over filling in baking dish; press crust onto edge of dish to secure. Edges of crust will hang over sides of dish. Tuck excess crust under sides of dish, if desired. Cut an "X" in top of dough for steam to escape. Place baking dish on an aluminum foil-lined baking sheet.
Bake at 450° for 16 to 20 minutes or until crust is golden brown. Let stand 10 minutes before serving.