Mix the the meatball ingredients together, omitting the cheese, in a large bowl with your hands until well combined. Preheat the oven to 425F. Line a sided cookie sheet with foil and set aside.
Slice the top and bottom off of an onion and peel off the skin. Cut the onion in half and now peel back the layers. Use the two sides of the onion and see how large you need to make your meatball. Stuff the meatball with the 1/2" cheese cube and roll into a ball. Insert your meatball in the onion halves and make sure it fits nicely, not too small or too large.
Wrap each of the onion bombs with 2-3 slices of bacon depending on the size of the bomb and secure with toothpicks. Bake on the prepared cookie sheet for 40 min. or until a thermometer reads 165F. Brush liberally with BBQ sauce and bake another 5-10 min.