Preheat the oven to 350ºF. In a small bowl whisk together the egg, milk, and Worcestershire sauce. In a separate small bowl, stir together the breadcrumbs, Italian seasoning, garlic powder, salt, and pepper. Mince the onion.
Add the ground beef, egg mixture, breadcrumb mixture, and minced onion to a large bowl. Use your hands to mix the ingredients together until evenly combined. Avoid over mixing.
Place the meatloaf mixture on a rimmed baking dish and shape it into a loaf that is approximately 4-inches wide, 8-inches long, and 2-inches tall.
In a separate small bowl, stir together the glaze ingredients (ketchup, brown sugar, Worcestershire sauce, and mustard). Spread the glaze evenly over the top and sides of the meatloaf.
Bake the meatloaf for 50-55 minutes, or until the internal temperature reaches 165ºF. Allow the meatloaf to rest for 5-10 minutes after baking, then slice and serve.