Slice your onion into thick, 1/2″ – 3/4″ slices.
Form the burgers into 8 equally-sized balls. Season the tops with salt and pepper.
Preheat your griddle or flat top or cast iron over medium-high to high heat.
Place the burger balls onto the grill, and immediately smash down with a burger smasher, bacon press, or heavy-duty spatula.
Cook for several minutes until a dark-brown crust forms, season the uncooked side of the burger, and then flip.
Top with cheese, cover with a melting lid (if necessary), and cook another couple of minutes until the bottom also has the crust formed.
Remove from the flat top and serve hot!
