Cook the macaroni as per package instructions until al dente.
In a large bowl, combine the diced chicken, celery, bell pepper, and red onion.
In a separate bowl, whisk together mayonnaise, Dijon mustard, apple cider vinegar, salt, and pepper.
Add the cooked macaroni to the chicken and vegetable mixture.
Pour the dressing over the salad and toss everything together gently.
Chill the salad in the refrigerator for at least 30 minutes before serving.
Before serving, garnish with chopped parsley for added color and freshness.