Prepare the Ingredients: Start by shredding the cooked chicken into bite-sized pieces. Dice the celery, halve the grapes, and chop the red onion and nuts if using.
Mix the Dressing: In a small bowl, combine the mayonnaise (or Greek yogurt), Dijon mustard, and lemon juice. Add salt and pepper to taste.
Combine the Salad: In a large mixing bowl, add the shredded chicken, celery, grapes, red onion, and nuts. Pour the dressing over the mixture.
Toss and Serve: Gently toss everything together until well-coated. If desired, garnish with fresh herbs like parsley or dill.
Chill and Serve: For the best flavor, chill the salad in the refrigerator for 30 minutes before serving.