Heat the oven: Preheat to 350°F. Line a rimmed baking sheet or a 9 x 13-inch baking dish with aluminum foil for easy cleanup.
Soak the oats: In a large bowl, whisk together the eggs, milk, Worcestershire sauce, salt, garlic powder, onion powder, and black pepper. Stir in the oats and let the mixture sit for about 5 minutes so the oats can absorb some of the liquid.
Mix the meat: Stir the grated onion into the oat mixture. Add the ground beef and use your hands or a fork to gently mix everything together just until combined. Do not over-mix.
Shape the loaf: Transfer the meat mixture to the prepared pan and shape it into a free-form loaf measuring approximately 9 x 5 inches. Press the loaf together firmly so it doesn't fall apart when you slice into it.
Whisk the glaze: In a small bowl, whisk together the ketchup, brown sugar, apple cider vinegar, Worcestershire sauce, and mustard.
Glaze the loaf: Spread a thin layer of the glaze over the top and sides of the meatloaf, reserving the remaining glaze.
Wrap in bacon: Arrange the bacon slices crosswise over the glazed meatloaf, overlapping them slightly. Cover the top, ends, and sides completely. Tuck the ends of the bacon underneath the loaf, trimming any very long strips with kitchen shears.
Bake uncovered: Bake the meatloaf for 50 minutes.
Glaze again and finish baking: Brush the reserved glaze over the bacon. It's fine if you don't use all of it. Return the meatloaf to the oven and bake for another 10 to 15 minutes, until an instant-read thermometer inserted into the center registers 160°F.
Broil for crisp bacon: For crispier bacon and a more caramelized glaze, place the meatloaf under the broiler for 1 to 3 minutes. Watch it closely, because the sugary glaze can burn quickly.
Rest before slicing: Let the meatloaf rest for at least 10 minutes before slicing.