Fennel, Cherry Tomato & Chicken Salad with Toasted Pistachios

few stems of fennel from the bulb you'll use for the salad below

slice onion

small stalk celery

boneless skinless chicken thighs (about 10 ounces)

Salt

Pepper

garlic, grated on a Microplane or minced with salt

red wine vinegar

Dijon mustard

olive oil

Salt

bulb fennel, core removed and very thinly sliced, preferably on a mandoline

cherry tomatoes

few handfuls of lettuce--green or red leaf, or romaine, chopped

toasted pistachios, coarsely chopped