Preheat oven to 350 degrees. In a large bowl combine beef, onion, parsley, Italian breadcrumbs, milk, Worcestershire sauce, eggs, garlic powder, salt and pepper. Use your hands to mix until combined being careful not to overmix. Press into a 9x5 inch loaf pan.
In a small bowl whisk together ketchup, vinegar and brown sugar. Brush half of the mixture on the top of the meatloaf.
Bake in preheated oven for 50 minutes. Brush the remaining glaze on top the last 10 minutes. Bake until the beef is cooked throughout and 160 degrees.