Preheat the oven to 425ºF with a rack in the center position. Place the chicken in a baking dish and season all over with the salt and pepper. Bake for about 20 to 25 minutes, or until it reaches an internal temperature of 165ºF on a meat thermometer. Allow to cool completely then slice.
Meanwhile, make the dressing. In a small bowl, whisk together the mayonnaise, olive oil, vinegar, lemon zest, lemon juice, honey, salt and pepper.
In a large bowl, toss the chicken, walnuts, celery, grapes and apples with the dressing.
To serve, place the lettuce on a serving platter and top with the chicken mixture.