Italian Pasta Bake

ground beef

large onion, chopped

garlic cloves, minced

jar (24 ounces) spaghetti sauce

(14-1/2 ounces) diced tomatoes, undrained

mushroom stems and pieces, drained

Italian seasoning

uncooked medium pasta shells

plum tomatoes, sliced

shredded provolone cheese

shredded part-skim mozzarella cheese