Preheat oven to 425 degrees F. Cut hot dogs in half lengthwise, and then slice into bite-size pieces. Chop onion.
Spread one can of chili over bottom of 13x9 inch pan. Open up three of the hot dog buns and lay on top of the chili, the fourth bun tear in half and fill in the gap at the bottom. Sprinkle the sliced hot dogs over the buns. Sprinkle 1 cup of the cheese over the hot dogs. Spread the other can of chili over the top of this. Cover with the chopped onion and the other 1 cup of cheese.