Spread a coating on mayonnaise on the inside of the hot dog buns.
Fill the buns with the hot dogs and place in a 9x 13 inch baking dish. You will have to squeeze then into the dish.
Top each dog with a Tablespoon of the relish.
In a pan, saute the butter and onion until tender. Add the chili to the onions and stir until well combined.
Top the dogs with the chili and sprinkle with cheddar cheese.
Cover with foil at bake at 350 degrees for 40 minutes.