Mix together the meat, egg, bread crumbs, cheese, basil, parsley, and green onions; shape into 3/4 inch balls. Pour broth into a large saucepan over high heat. When boiling, drop in meatballs. Stir in escarole, lemon zest and orzo. Return to a boil; reduce heat to medium. Cook at a slow boil for 10 minutes or until orzo is tender, stirring frequently.