Cook the bacon in a skillet over medium heat, stirring occasionally, until crisp, about 8 minutes. Remove with a slotted spoon; set aside. Pour off all but 1 tablespoon of the drippings. Add the onion to the skillet; saute until soft, about 8 minutes. Let cool.
Preheat the oven to 375 degrees F. Combine the bacon, onion, beef, panko, cheese, eggs, 2 tablespoons barbecue sauce and the parsley in a large bowl; season with salt and pepper and mix with your hands until just combined.
Spray a 12-cup muffin pan with cooking spray. Pat the meat into each muffin cup to just below the top. Spread 1/2 tablespoon barbecue sauce on each. Bake until cooked through, 12 to 15 minutes. Let cool in the pan.
Meanwhile, butter the buns and toast cut-side down in a skillet over medium-high heat. Sandwich the meatloaves on the buns; top with pickles and serve with extra barbecue sauce.