Stir soup, gravy and milk in bowl. Layer half the potatoes, onion, ham and soup mixture in 13x9x2" shallow baking dish. Repeat layers. Cover.
Bake at 375 degrees F for 40 minutes. Uncover and bake 25 minutes. Top with cheese. Bake 5 minutes more or until potatoes are tender and cheese melts. Let stand 10 minutes.