1. Preheat oven to 350 degrees F (175 degrees C).
2. Lightly grease a 9x13 inch baking dish. Toss the tators in, Pour the chili over the tators, sprinkle with the chopped onion, then spread some mustard over the chili and the onion. Top off with the cheese.
Bake at 350 degrees F (175 degrees C) for 30 minutes.