Preheat your oven to 350°F.
In a large mixing bowl, combine the ground beef, breadcrumbs, chopped onion, milk, eggs, Worcestershire sauce, garlic powder, salt, and black pepper. Mix until just combined; do not overmix.
Transfer the meat mixture to a loaf pan, shaping it into a loaf.
In a small bowl, mix together the ketchup, brown sugar, and mustard. Spread half of this mixture over the top of the meatloaf.
Bake in the preheated oven for 1 hour. After 30 minutes, spread the remaining ketchup mixture on top.
Continue baking until the internal temperature reaches 160°F.
Let the meatloaf rest for 10 minutes before slicing. Serve warm.