Wash the lettuce, tomato, and onion thoroughly and slice them.
Shape the beef patty into a round shape and season with salt and pepper.
Heat oil in a pan and grill the patty on both sides.
Cut the hamburger bun in half, spread butter on the inside, and toast lightly in the pan.
Layer the patty, cheese, lettuce, tomato, onion, and sauce on the bottom bun in order.
Place the top bun on and finish.