Place the chicken in a medium deep skillet and cover with water. Add a pinch of salt, cover, and bring to a simmer over medium-high heat. Once simmering, reduce heat to low and let simmer for 7-10 minutes or until chicken is cooked through and no longer pink inside. Transfer to a cutting board and shred with two forks. Transfer the chicken to a plate and place in the refrigerator to chill for at least 15 minutes.
While chicken chills, place a small skillet over medium-high heat. Once skillet is heated, add in the walnuts and let toast for 5 minutes or until fragrant and starting to brown. When cool enough to handle, roughly chop and set aside.
Also, combine all of the ingredients for the fayonnaise together in the bottom of a large mixing bowl and whisk until combined. Set aside.
Add the apple, chicken, celery and walnuts to the large bowl with the fayonnaise. Toss to combine thoroughly.
Lay out your lettuce cups and fill with the waldorf mixture. Serve.