Mix ground beef, barbecue sauce, garlic powder, black pepper, and salt in a large mixing bowl using your hands. Shape into 12 thin patties and refrigerate covered.

Cook bacon in a skillet over medium-high heat until browned, about 5 minutes. Drain bacon on paper towels. Reduce heat to medium, cook onions in bacon drippings until soft. Mix bacon and onions in a bowl.

Preheat an outdoor grill for medium heat and lightly oil the grate.

Remove beef patties from refrigerator; top six patties with 1-1/2 tablespoons of the bacon-onion mixture and shredded cheese. Cover each with another patty and seal edges.