Prepare The Chicken: If your chicken is not pre-cooked, poach or grill the chicken breasts. Once cooked, allow them to cool, and then shred them into bite-sized pieces.
Mix The Salad: In a large bowl, combine the shredded chicken, mayonnaise, chopped celery, halved grapes, chopped nuts, and thinly sliced green onions.
Season: Add Dijon mustard, lemon juice, salt, and black pepper to the salad. Mix well to ensure all ingredients are evenly coated.
Chill: For the best flavor, cover the salad and refrigerate it for at least 1 hour. This allows the flavors to meld together.
Serve: Serve the chicken salad on a bed of lettuce leaves or mixed greens. Garnish with fresh dill or parsley if desired.