Preheat your grill on high for at least 10 minutes.
Divide the ground beef into 4 equal (6 oz) portions on a flat surface, then divide each of those in half (so you should have 8, 3 oz portions). Use your hands to flatten each into a ¼-inch thick round patty.
Place 2-4 tbsp of cheese in the center of 4 of the patties, then place the remaining 4 patties on top. Carefully press the edges together to seal in the cheese and carefully fold the edges in (watch the video). Sprinkle salt and pepper all over.
Grill the burgers, covered, for 8-10 minutes or until cooked through, flipping halfway. Place your buns on the grill during the last few seconds to lightly toast them. It’s best to let your burgers rest for 10-15 minutes for the juices to redistribute.
Assemble your burgers starting with lettuce (if using), burger patty, BBQ sauce, and caramelized onions. I recommend cutting the burgers in half before eating (some cheese may ooze out, but you can dip/wipe your burgers in it on your plate).