In a large soup pot drizzle olive oil and adjust heat to a medium setting. add chopped onion and saute, adding in the salt, basil, oregano, black pepper and red pepper flake if desired. Stir for a couple of minutes. Add garlic and stir to combine. Add the tomato paste and then the diced tomatoes and chicken stock. Stir and simmer for approximately 15 minutes. (You may puree the soup if desired with an immersion blender, if desired). Add the meatballs and cooked rigatoni, then simmer uncovered for a few minutes.
