Brown your ground beef, drain and add spaghetti sauce. Put Aside. Boil your rigatoni according to package directions, drain. Add a little of the sauce in the bottom of your 9x13 in pan, then half your rigatoni noodles, on top add a layer of cottage cheese, grated cheddar cheese, them a 4 oz can of drained chopped mushrooms. More sauce, rigatoni, cottage cheese, More sauce then grated cheddar cheese on top. bake at 350 for 30 minutes or til heated through.