Heat a grill or grill pan to medium high. Season meat with salt and pepper, mix very lightly, and shape into four patties. Grill hamburgers 4 to 6 minutes per side for rare and 9 to 11 minutes for well done. If making cheeseburgers, lay cheese slices on top of the hamburgers after they have been flipped.
Serve immediately on buns (toasted, if desired), topped with tomatoes, lettuce, and onion slices.