Hand mix the ground pork with the onions, shredded cheese and bbq sauce
Form into 4 patties. Coat with the BBQ rub. Press a "thumb divot" into one side of each patty to reduce the amount of puffing up in the center.
Heat grill to 400-450. Grill the patties to 140 degrees, flipping occassionally. Put the cheese slices on for the last minute to get them melted. Optional: glaze the patties with a bbq sauce for the last few minutes, prior to putting on the cheese slices. This should be done when they reach about 120 degrees.
Warm the buns. We like to put a coating of margarine or mayo on each slice and then broil them for a few minutes. The air fryer also does a great job.
Build the sandwiches and serve.