Preheat the oven to 350°F.

In a medium mixing bowl, combine ground beef, oatmeal, milk, egg, onion, salt, and pepper. Incorporate everything into the meat with your hand. This only takes about 30 seconds. You don't want to over-mix the ingredients.

Place the meat in a large loaf pan and press it down evenly.

In a small bowl, combine the ketchup, brown sugar, and mustard for the glaze. Pour over meatloaf evenly.

1 hour and 20 minutes at 350 degrees.

Remove from oven and set aside to drain any excess grease. Allow for 5 minutes before serving.