Get the grill pan very hot. Oil grill where the burgers go. Place a ball of meat (1/3 lb or 1/6 lb for thinner burgers / see note) on the hot grill and mash a little with a sharp spatula.
Place a small handful of very thinly sliced ​​onions on top, then smash the burger the rest of the way, crushing the onions into the meat.
Season the top with salt and pepper and cook. Don’t mess with that.
When the bottom is dark brown and the burger is almost done, scrape it under the burger to get the “skin” and turn it over.
Continue to cook for 1-2 more minutes. Top with cheese and melt for about 1-2 minutes more. *While the cheese is melting, you can place the buns, cut them on the grill to toast.
Place the burger on the bottom bun, dress it how you like it, place it on the top bun, and dig in! Enjoy!