01 - In a large bowl, mix the cooked chicken, celery, red onion, grapes, and nuts if using.
02 - In a small bowl, whisk together mayonnaise, Greek yogurt, Dijon mustard, lemon juice, salt, and pepper until smooth.
03 - Pour the dressing over the chicken mixture and toss gently to coat evenly.
04 - Fold in the chopped parsley carefully.
05 - Cover and refrigerate the mixture for at least 15 minutes to allow flavors to meld.
06 - Serve scoops of the salad on lettuce leaves, with crackers, or as a sandwich filling.