Pack the beef tightly together with your hands, and then shape it into a 4-inch-diameter patty on a sheet of wax paper. Sprinkle lightly with salt on both sides, and then place in the freezer for 5 minutes (to help the patty keep its shape).

Preheat a grill to high.

Cut the whole bacon strip in half crosswise. Lay the 3 half strips side by side in a small nonstick skillet over medium heat. Cook, flipping them every couple of minutes, until crispy and well done, 6 to 8 minutes. Transfer the bacon to a paper towel-lined plate to drain.

Meanwhile, remove the patty from the freezer and place it on the grill. Cook for 1 to 2 minutes per side for medium rare, or until the desired doneness is reached. Toast the bun halves on an upper grill rack for 30 seconds to 1 minute, watching them carefully. Place the cheese on top of the burger for the last few seconds of cooking so it just begins to melt.

Add the patty to the toasted bun bottom. Lay the bacon strips side by side over the top. Place the onion over that. Spread the barbecue sauce evenly over the inside of the top half of the bun. Place the bun top atop the sandwich. Serve immediately.