In a large bowl, add the cooked and chopped chicken, chopped celery, halved grapes, dried cranberries, chopped roasted pecans, and (if using) chopped celery leaves.
Add the mayonnaise (or Greek yogurt), salt, and black pepper to the bowl.
Using a large spoon or spatula, gently mix all the ingredients together so the grapes don’t get crushed.
Taste and add more salt or black pepper if needed.
If you like, cover and refrigerate the salad for 30 minutes to let the flavors blend.
Serve the salad chilled—on a bed of lettuce, in sandwiches or wraps, or with crackers. Garnish with extra pecans, grapes, or fresh herbs if desired.