Toss the diced apple with the lemon juice in the bottom of a large bowl. Add the kale, celery, walnuts, and dried cranberries. Toss to combine. In a separate bowl, whisk together the olive oil, vinegar, honey, and mustard until emulsified. Pour over the salad and toss to combine. Season to taste with salt and pepper. Refrigerate for 1 hour before serving.
Notes
Make It a Meal: Serve topped with sliced grilled chicken.