Spray a nonstick frying pan with cooking spray. Add the onion slices and sauté for up to 10 minutes, stirring occasionally.
Season the shaved steak with garlic powder, onion powder, salt, and pepper.
Push the onions to the side and add the shaved steak to the pan. Cook for 1-2 minutes, or until the beef is no longer pink.
Place the hamburger bun on a baking sheet. Top the bottom bun with the shaved steak, followed by the onions, and a slice of cheese. Leave the bun open and place under the broiler for 2 minutes, or until the cheese is melted and the top bun is toasted.