In a small bowl, mix together the mayonnaise, ketchup, dill pickle relish, and Dijon mustard to make the sauce. Set aside.

Divide the ground beef into 4 equal portions and form into patties. Season with salt and pepper.

Heat a grill or skillet to medium-high heat. Cook the patties for about 3-4 minutes on each side for medium-rare, or until cooked to your liking.

A minute before the burgers are done, place a slice of cheddar cheese on each patty to melt.

Spread the sauce on the bottom halves of the toasted buns. Place the burger patties on the buns, then top with lettuce, tomato slices, and red onion rings. Cover with the top halves of the buns.