Fry the beef with the onion in it (diced). Drain the fried beef. Add the cheese, cream of mushroom soup and mix. Put this mixture in a greased casserole dish. Place halved biscuits on the top of the mixture but leave enough space in-between them so they can cook properly. Bake at 350 for an hour. You can bake any leftover biscuits on a separate pan and serve with the casserole.