Start by cooking your chicken until it's tender and fully cooked, about 15-20 minutes. Once cooled, shred the chicken into bite-sized pieces for a perfect texture.

In a large bowl, combine mayonnaise, Greek yogurt, mustard, and a pinch of salt. Mix well until smooth and creamy.

Gently fold in the shredded chicken along with diced celery, grapes, and walnuts.

Cover the bowl with plastic wrap and refrigerate for at least 30 minutes.

While the mixture chills, wash and cut your lettuce leaves into sturdy cups.

Spoon generous amounts of the chilled chicken salad into each lettuce cup just before serving.