Combine ingredients. Preheat the oven to 350°F (175°C). In a large mixing bowl, add the ground beef, onion, garlic, egg, ketchup, Worcestershire sauce, oats, milk, parsley, Italian seasoning, salt, and pepper. Using your hands, mix together the ingredients until well combined, but try not to over-mix.
Divide the mixture. Grab a small handful of the mixture and lightly roll it between your hands, then place it in the muffin pan. Repeat this process until the mixture is evenly divided between all 12 muffin cups. Note: I like to keep the muffins just slightly rounded, so that any grease from the meat stays on the outside edges.
Coat with the glaze. In a small bowl, stir together the ketchup, Worcestershire sauce, and sugar. Spoon it over the top of each meatloaf muffin. Alternatively, you can glaze the muffins after they've come out of the oven.
Cook. Place the muffin tray in the oven and cook for 25 to 30 minutes, or until the internal temperature has reached 160°F (70°C).
Serve. Remove the meatloaf from the oven and let it rest for a few minutes, then serve with your favorite sides (see ideas above!)