Preheat the grill for 20 minutes on medium heat with the lid down. If you don't have a grill, you can also prepare these delicious burgers on the stovetop. Just fry the burgers in some butter in a frying pan for a few minutes on each side.

In a bowl, combine the ground beef, salt, and pepper.

Finely chop the onion and cut the jalapeño into small pieces. Remove the seeds first if you don’t want it to be too spicy. Add onion and jalapeño to the meat and combine thoroughly with your hands.

Form one hamburger patties per portion. First, shape them into a ball and then slowly press down. If you make them on the grill, leave them a bit thicker because they cook fast.

Grill the patties for 5-7 minutes on each side, depending on how well done you want them. Allow them to rest for 10 minutes before serving so the juices can settle.

While the burgers are on the grill, thinly slice the tomato. Cut the avocado lengthwise, remove the pit and spoon out the flesh.

To assemble, take 3-4 lettuce leaves for each burger. Place burger in the middle, top each with slices of cheese and a slice of butter. Add the tomato and avocado, season with salt and pepper. Try to wrap the burger so you can easily grab it.