I mention using a food processor but you can just chop everything by hand, just make sure it's chopped very fine.
In a food processor add your white onion and garlic and pulse a few times. Then break up your cooked bacon and pulse again. Add your ground meat pulse, add egg, pulse until combined well. If meat is warm or room temperature then place in the fridge for a few minutes. Using your hands make 5 large meatballs the size of baseballs or you can make 10 small golf ball sized meatballs. In a large skillet warm some oil and brown each side of the meatballs, place in a baking dish and bake for about 15 minutes in the oven. You may need to bake less or more depending on the size you choose to make.