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 meat 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.