Add all ingredients to a large bowl and mix everything together.
4 cups chopped rotisserie chicken, 1 cup chopped celery, 1 cup red grapes, halved, 1/2 cup diced red onion, 1/2 cup diced cucumber, 1/2 cup walnuts, 1/2 cup mayonnaise, 1/2 cup Greek yogurt, 1/4 cup chopped green onions, 2 tbsps. chopped fresh parsley, 1 tsp. Dijon mustard, 1/2 tsp. dried dill, 1/2 tsp. kosher salt, 1/2 tsp. black pepper