Preheat oven to 375°F (190°C).
In a bowl, combine ground beef, breadcrumbs, egg, chopped onion, garlic powder, salt, and pepper.
Roll the mixture into small meatballs and place on a baking sheet.
Bake for about 20 minutes, or until cooked through.
2. Make the Sauce
In a saucepan, combine ketchup, brown sugar, vinegar, soy sauce, and garlic powder.
Bring to a simmer over medium heat and cook until the sauce thickens slightly, about 5–7 minutes.
3. Combine and Serve
Toss the baked meatballs in the sweet and sour sauce, coating them evenly.
Serve hot with steamed rice or as an appetizer.
