Combine chicken broth, chicken, carrots, apple, onion, celery, Parmesan cheese, and bay leaf together in a large pot. Bring to a boil, reduce heat to medium-low, and simmer until vegetables are soft, about 30 minutes.
Stir orzo into broth mixture. Cook, stirring occasionally, until orzo is cooked through but firm to the bite, about 11 minutes.
