Mix ground beef, egg, salt and pepper, garlic powder, onion, oats, and breadcrumbs in a mixer (You can also mix this by hand but it's so much easier using a KitchenAid!)
Put meat mixture in meatloaf pan (or a regular loaf pan).
In a separate bowl, combine ketchup, Worcestershire sauce and ground mustard. Mix well.
Set aside about 1/2 a cup of the sauce for dipping if you wish. Pour the rest of the sauce on to the meatloaf and use the back of a spoon to spread it evenly throughout the meatloaf's surface.