Preheat oven to 350°F (175°C).
In a large bowl, combine ground beef, breadcrumbs, milk, egg, onion, green pepper, salt, and black pepper. Mix well.
Shape the mixture into small meatloaf balls and place them in a baking dish.
In a small bowl, mix together ketchup, brown sugar, and mustard. Pour this sauce over the meatloaf balls.
Bake in the preheated oven for 30-35 minutes, or until cooked through.
Serve the meatloaf balls hot with your favorite sides.
