Start by finely shredding the cooked chicken breast. If you prefer a smoother texture, use a fork to mash the chicken until it reaches your desired consistency.
In a large bowl, combine the Greek yogurt, light mayonnaise, Dijon mustard, and lemon juice. Mix until smooth and well blended.
Add the finely shredded or mashed chicken, celery, red onion, and parsley to the bowl with the dressing. Stir until all ingredients are evenly coated.
Season and add crunch (Optional): Season with salt and pepper to taste. If desired, mix in the chopped walnuts or almonds for a bit of extra crunch.
Cover the bowl and refrigerate for at least 30 minutes to allow the flavors to meld together. Serve chilled on a bed of lettuce, in a whole grain wrap, or with your favorite healthy crackers