Combine stock, barley and bay leaf. Bring to boil; reduce heat, cover and simmer for 40 minutes.
Stir in carrots and celery; cook for 5 minutes or until stock is absorbed and barley is tender.
Discard bay leaf; transfer to large bowl. Fluff with fork. Meanwhile, chop onions and green pepper; drain and rinse beans. Add to barley mixture.
Dressing:
Whisk together stock, vinegar, mustard, basil and thyme; whisk in oil. Toss with barley mixture. Refrigerate for at least 2 hours or for up to 8 hours. Stir in parsley. Serve on lettuce leaves.