Prepare the chicken. Use cooked and cooled chicken. Shred it into bite-sized pieces or dice it neatly. (Tip: shredding with two forks makes it tender and easy.)
Chop the mix-ins. Dice celery, onion, and grapes (or apple). Keep them small for even bites.
Make the dressing. In a large mixing bowl, whisk together mayonnaise, Greek yogurt, Dijon mustard, lemon juice, garlic powder, salt, and pepper until smooth and creamy.
Combine everything. Add the chicken, celery, onion, grapes, and nuts (if using) into the bowl with the dressing. Stir gently until everything is evenly coated.
Chill. Cover and refrigerate for at least 30 minutes before serving. This helps the flavors meld together.
Serve. Enjoy chicken salad on sandwich bread, croissants, crackers, or lettuce wraps.