Meanwhile, in a large saucepan stir together the water, garbanzo beans, beef broth, undrained tomatoes, green beans, mushrooms, Italian seasoning, and, if desired, fennel seed. Bring mixture to boiling; reduce heat. Cover and simmer for 10 minutes. Stir in the meatballs; simmer for 15 minutes until meatballs are thoroughly heated (165º F) To serve, ladle into soup bowls.