In a large saucepan combine chicken broth, water, turkey, carrots, onion, celery, and, if using, dried thyme. Bring to boiling; reduce heat. Simmer, covered, for 15 minutes.
Stir in noodles and squash. Cook, uncovered, for 10 to 12 minutes or until noodles are tender. Stir in lemon juice and, if using, fresh thyme. Cook, uncovered, for 1 minute more. Makes 5 servings.