How to Make It
Heat the oven to 350°. Toast the walnuts until golden brown, about 8 minutes. Let cool.
In a large frying pan, cook the bacon until it is crisp. Drain the bacon on paper towels and then crumble it.
In a small glass or stainless-steel bowl, whisk the vinegar with the mustard, salt, and pepper. Whisk in the oil.
In a large bowl, combine 2 tablespoons of the dressing with the chicken. Let sit for about 5 minutes so that the chicken absorbs the dressing. Add the walnuts, bacon, spinach, onion, apple, and the remaining dressing and toss.
Warm garlic bread, served either plain or with a little Parmesan cheese, goes well with all the flavors here.