Simple do-ahead steps make this salad perfect for a summer picnic or backyard barbecue. It’s refreshing and brightly colored, with the sweetness of the apples playing off the tang of the creamy lemon dressing. With a sharp knife you can quickly make matchsticks from the carrots and apple. A faster approach, and perfectly satisfactory, would be to use the coarse grating disk of a food processor. The napa cabbage, however, looks best when cut by hand.