Preheat oven to 375 degrees F (190 degrees C).
Combine Ground Beef (1.5 pound), Egg (1), Salt (1 teaspoon), Freshly Ground Black Pepper (1/2 teaspoon), Garlic Powder (1 teaspoon), Onion (1/2), Oats (1 cup), and Panko Breadcrumbs (1 cup) in a mixer or by hand.
Put meat mixture in meatloaf pan or a regular loaf pan.
In a separate bowl, combine Ketchup (1 1/2 cup), Worcestershire Sauce (2 tablespoon), and Dry Mustard (2 teaspoon). 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.
Bake for 45 minutes.
Let the meatloaf rest for about 10 minutes before you transfer it to a serving dish. Serve with your favorite side dish! Enjoy!