Preheat oven to 350 degrees F. Line a 9×13 baking dish with foil and coat with cooking spray. Heat the chili till warm in microwave or on stovetop. Cook hot dogs over medium heat on a grill until warmed through (alternatively, cook for 1 to 2 minutes in microwave).
Place the hot dogs in the buns and place in a single layer in the prepared baking dish. Top with chili and cheese and bake in the preheated oven for 25 minutes, or until cheese is melted.
Top with chopped tomatoes and onions and serve immediately!