In a large mixing bowl, combine the shredded rotisserie chicken, halved grapes, chopped celery, and sliced almonds.
In a separate small bowl, whisk together the mayonnaise, Dijon mustard, lemon juice, garlic powder, salt, and pepper until smooth.
Pour the dressing over the chicken mixture and gently toss until everything is well coated.
If using, fold in the chopped parsley for added flavor and color.
Cover the bowl with plastic wrap and refrigerate for at least 30 minutes to allow the flavors to meld.
Serve the chicken salad on a bed of greens, in a sandwich, or in a wrap as desired.