Season ground beef with salt and pepper to taste. Form it into patties. Set aside.
Fry sliced onion on olive oil and cook over low heat until a golden brown color is reached
Prepare the burgers in preheated grill, over medium heat. Flip until browned in all sides and let cook for about 5-10 minutes per side. For well done the temperature inside should be at least 155 °F.
Assemble burgers with meat, lettuce, tomato, caramelized onions, cheese and sauces as desired.
Recipe Notes
Consider using Hawaiian buns to give the burger a little sweet taste.