Oklahoma onion burger is prepared by smashing thin slices of onions into a beef patty. The meat and onions cook together until the onions become caramelized and crispy and the meat is fully cooked. The burger usually also contains a slice of American cheese, pickles, and mustard or mayonnaise (or both), all tucked inside soft and fluffy burger buns.

It is believed that this burger was invented in the 1920s during the Depression, when onions were very cheap, and meat was expensive, so people started to add onions to the patties by smashing them into the meat with the back of a spatula.