Put 1/2 sauce in bottom of 9 x 13" pan. Layer raw noodles, 1/2 hamburger, onion and part of cheese.
Place American cheese on top of this. Next 1/2 of sauce, noodles, cheese and meat. Last, 1/3 of sauce and parmesan cheese and press down slightly. Pour 1 1/2 cup of hot water over top.
Bake 1 hour covered and 1/2 hour uncovered. Let stand 15 minutes before serving.