Prep the Chicken: If using leftover roasted chicken, shred or chop it. If cooking fresh, roast a chicken with salt, pepper, and a little olive oil, then let it cool.
Mix Veggies and Nuts: In a large bowl, combine celery, apple, red onion, and walnuts.
Make the Dressing: In a separate bowl, mix Greek yogurt, mayonnaise, Dijon mustard, honey, salt, and pepper until smooth. Taste and adjust seasoning.
Combine: Add the chicken to the veggie-nut mix. Pour in the dressing and fold gently until everything is coated. Don’t overmix.
Chill (Optional): Let the salad sit in the fridge for 30 minutes to allow flavors to blend.
Serve: Garnish with fresh parsley or dill if desired. Serve on its own, over greens, in a sandwich, or with crackers.