In a large skillet, heat the olive oil. Add the onion, crushed red pepper and the remaining garlic and cook over moderate heat until the onion is softened, about 4 minutes. Add the tomato and cook, stirring occasionally, until saucy, about 5 minutes. Add the meatballs, cover and cook over moderately low heat, carefully turning the meatballs a few times, until firm and cooked through, about 10 minutes. Using tongs, transfer the meatballs to a rimmed baking sheet to cool.