Heat a nonstick skillet to medium high heat. Add sliced onions and cook on high for about 5 minutes. Turn the heat to medium low for another 5 minutes. Add steak sauce and stir. Let simmer until ready to use.
Form the ground beef into 4 patties and season each side with salt and pepper. Preheat outdoor grill or grill pan on stovetop. Cook burgers about 5 minutes per side. Add cheese on the patties when there is one minute left to cook.
Top cheeseburger patties with onions and tomatoes.