How to Make It
Make 3 deep slashes in each chicken breast. In a small bowl, mash the garlic, fennel, 2 teaspoons of salt and 1/2 teaspoon of pepper. Stir in 3 tablespoons of the oil. Rub the mixture all over the chicken and into the slashes. Transfer to a small roasting pan, cover and let stand for 1 hour.
Preheat the oven to 350°. Spread the walnuts in a pie plate and toast for 10 minutes, until browned and fragrant. Let cool.
Roast the chicken for about 40 minutes, until cooked through. Let cool slightly, then discard the skin and thinly slice the meat.
In a food processor, blend the vinegar with the mustard and the remaining 1/4 cup of oil. Blend in the cheese and buttermilk. Transfer to a bowl, stir in the lemon zest and season the dressing with salt and pepper.
In a large bowl, combine the chicken with the walnuts, grapes, apples, celery, mesclun, parsley, tarragon and chives. Add the dressing, toss well and serve.