Prep the chicken: Make sure the cooked chicken is cool, then shred or chop into bite-sized pieces.
Chop the mix-ins: Dice apples, cucumbers, grapes, and walnuts into small pieces for even texture.
Make the dressing: In a bowl, combine mayonnaise (or yogurt), Dijon mustard, lemon juice, salt, and pepper. Whisk until smooth.
Mix it all together: In a large mixing bowl, add chicken and your chopped mix-ins. Pour the dressing on top and stir gently to combine.
Chill the salad: Cover and refrigerate for at least 30 minutes to let the flavors blend.
Serve your way: Enjoy in sandwiches, lettuce wraps, meal prep bowls, or straight from the bowl!