Preheat a cast iron skillet over medium-high heat until very hot.

Place the ground beef balls in the skillet and immediately smash them down with a spatula to form thin patties.

Cook for about 2-3 minutes until a crust forms, then flip the patties.

Add a slice of cheese on top of each patty and cook for an additional minute until the cheese melts.

Toast the burger buns in the skillet until golden brown.

Spread mayonnaise on the bottom bun, then add the lettuce, tomato, and the cooked patty.

Top with ketchup and mustard, then place the top bun on.