In a mixing bowl, season the ground beef with salt and pepper. Divide it into 4 equal portions and shape them into balls.
Heat a large skillet or griddle over medium-high heat. Once hot, place the beef balls on the skillet and smash them down using a spatula to shape them into thin patties.
Cook the patties for about 3-4 minutes or until browned on the bottom. Flip the patties and add a slice of cheese to each one. Cook for an additional 2-3 minutes until the cheese is melted.
While the burgers are cooking, in a small bowl, mix together the mayonnaise, sugar-free ketchup, and yellow mustard to create a special sauce.
Remove the cooked patties from the skillet and let them rest for a minute.
To assemble the burgers, place a lettuce leaf as the base, add a patty with melted cheese, top with sliced pickles, diced onions, and the special sauce. Add another lettuce leaf on top to finish.
Optionally, sprinkle with sesame seeds for extra flavor and presentation.