Cut the onion in half. Mince one half and cut the other into slices.

In a bowl, put the minced onion with the ground beef, Worcestershire sauce, parsley, salt and pepper and combine well with your hands then divide into 4 patties.

Insert a cube of cheddar into the center of each patty. Make sure the cheese cube is entirely covered by the meat. Reshape the patties into even circles if needed.

Slightly brush the patties with oil and grill for 10 minutes then flip them over to cook the other side.

In the meantime, cut the hamburger buns open and brush the inside of each half with oil and grill until toasted.

Take the bottom part of the hamburger bun; place one grilled meat patty on it, then some tomato slices on it followed by some onion slices and a lettuce leaf. Then cover with the other half of the bun.

Repeat for the other buns.