In a large skillet, cook beef, bacon and onion. Stir occasionally until meat is browned and onion is tender and drain off the fat. In a 3-quart casserole dish, combine the three cans of beans, brown sugar, water, ketchup, vinegar and mustard. Stir in meat mixture until well combined.
Cover and bake for 45 to 50 minutes at 350 degrees, or until heated through.