Preheat the grill to high temperature.
From meat create 12 patties, about 5 cm wide.
Spice the patties with salt and pepper, bake them for 4-5 minutes and carefully turn on the other side.
Fill them equally with cheese, cover the grill and cook for an additional 4 minutes.
Remove the patties from the grill and toast buns for 1-2 min until they become dark.
To assemble the burgers, apply mayonnaise on the bottom bun. Add to that a patty, lettuce, onion and tomato. On the upper bun, put the ketchup. If necessary, use a toothpick so the burger would not fall apart.