Start with pre-cooked chicken. You can use rotisserie chicken or boil some chicken breasts until fully cooked. Allow it to cool, then shred or chop into bite-sized pieces.

In a large mixing bowl, combine the mayonnaise and Dijon mustard. Stir well until smooth and creamy.

Toss in diced celery, red onion, and grapes (or apples if using) into the dressing mixture. Mix until everything is evenly coated.

Gently fold in the shredded chicken, ensuring every piece is covered with the dressing. Season with salt and pepper to taste.

You can serve this chicken salad immediately, or for the best flavor, let it chill in the fridge for about 30 minutes. Serve it over a bed of lettuce or in a sandwich!