Preheat your oven to 350°F.
Chop the onion and bell pepper finely. Mince the garlic cloves.
In a large mixing bowl, combine the ground beef, gluten-free breadcrumbs, and grated Parmesan cheese. Add the chopped onion, bell pepper, and minced garlic. Crack in the eggs and pour in the milk and Worcestershire sauce. Sprinkle in the dried oregano, salt, and black pepper. Mix until well combined.
Transfer the mixture into a loaf pan and shape it into a loaf form.
Spread the ketchup evenly over the top of the meatloaf.
Bake for 60 minutes or until the internal temperature reaches 160°F.
Let the meatloaf rest for 10 minutes before slicing.