In a large stockpot heat chicken broth to boiling; stir in the spinach, pasta, and carrots (and onion and bay leaf if used). (Optional: Sautee carrot and onion before adding to broth.) Return to boil; reduce heat to medium. Cook, stirring frequently, at a slow boil for 10 minutes or until pasta is al dente. Add meatballs.. Serve hot with Parmesan cheese sprinkled on top.