Divide the ground beef into 4 equal loose balls of about 4 oz each, handling them as little as possible.

Heat the oil in a large cast-iron skillet over medium-high heat. Place 2 balls in the skillet, smash flat to about 1/4 inch thick, and cook without moving for 2 minutes until the edges are dark and crisp.

Flip the patties, top each with a slice of cheese, and cook another 1 to 2 minutes until melted and the underside is golden. Repeat with the remaining 2 balls.

Assemble each burger by layering lettuce leaves, a patty, pickles, mustard, and tomato, then fold and serve immediately.