To prepare salad, cook pasta in boiling water 11 minutes or until al dente. Add green beans during final 5 minutes of cooking. Drain and rinse pasta mixture under cold water. Place pasta mixture, chicken, celery, bell pepper, and onion in a large bowl; toss gently to combine.
To prepare dressing, combine 2 tablespoons water and remaining ingredients, stirring with a whisk. Drizzle over pasta mixture, tossing gently to coat.