In a mixing bowl, combine the mayonnaise, sugar-free ketchup, yellow mustard, dill pickle relish, onion powder, garlic powder, salt, and black pepper. Mix well to create the Big Mac sauce. Set aside.

Preheat a large skillet or griddle over medium-high heat.

Divide the ground beef into four equal portions (about 4 ounces each). Roll each portion into a ball and place them on the hot skillet.

Using a spatula, smash each beef ball down to form a thin patty. Cook for about 3 to 4 minutes on one side until a nice crust forms.

Flip the patties and immediately place a slice of cheddar cheese on each patty. Cook for an additional 2 to 3 minutes until the cheese is melted and the burgers are cooked to your desired doneness.

While the burgers are cooking, prepare the lettuce leaves by rinsing and drying them. These will act as your 'buns'.

Once the burgers are cooked, assemble each burger by placing a lettuce leaf down as the bottom bun. Add a patty with melted cheese on top, followed by a spoonful of Big Mac sauce, sliced pickles, and sliced onions. Top with another lettuce leaf as the 'top bun'.

Repeat the assembly for each burger and serve immediately.