Properly-poached chicken breast is truly a thing of beauty—juicy, tender, and a blank canvas for big flavors. And if your only experience with poached chicken is the dry-as-a-bone stuff from the salad bar, then this method will be a revelation. The trick is to cook the chicken very low and slow, so paying attention to your heat level is of the utmost importance. Add some crunchy veggies and a punchy Dijon vinaigrette, and you've got exactly the kind of simple, satisfying composed salad you need when a reset dinner is in order.
Cover 2 large chicken breasts with 4 cups cold water in a large saucepan. Season with 3 Tbsp. Diamond Crystal or 3½ tsp. Morton kosher salt. It sounds like a lot, but most of it will be discarded in the end, and well-seasoned poaching water is the key to flavorful chicken breasts.
Bring to a gentle boil over medium heat, then immediately turn chicken with tongs. Cover pot with a tight-fitting lid, remove from heat, and let sit until an instant-read thermometer inserted into the thickest part of breast registers 150°, 5–10 minutes (depending on thickness of the breast). Transfer chicken to a cutting board and let rest 10 minutes.
Meanwhile, make the dressing. Cut 1 lemon in half and squeeze cut side up into a medium bowl. Whisk in 2 Tbsp. Dijon mustard. Whisking constantly, very slowly stream in 6 Tbsp. olive oil until dressing is thick and emulsified. The word “slowly” is key here—if you add the oil all at once, you won’t get the creamy, nicely incorporated vinaigrette you’re after. Season with salt and pepper.
Trim ends off of 8 oz. green beans and transfer to a large resealable plastic bag. Seal bag and whack beans with a rolling pin to split the skins and soften the insides without completely pulverizing the flesh.
Drizzle 2 Tbsp. dressing into bag. Massage with your hands to break beans down further and coat. Season with salt and let sit at room temperature until ready to use.
Slice 1 small bunch chives into 2"-long batons. Transfer to a medium bowl. Separate lettuce leaves from 1 large head of Bibb lettuce and add to bowl with chives. Add 1 cup basil and toss to combine. Arrange on one side of a large platter. Cover lettuce and herbs with damp paper towels and chill until ready to use.
Rinse 1 bunch radishes, trim, and slice in half (or into ½" wedges if large). Tear 1 cup whole peperoncini into bowl. Mix in 1 Tbsp. dressing; season with salt. Let sit at room temperature until ready to use.
Slice chicken into ¼"-thick slices. It might be the tiiiiniest bit pink inside, which is okay! Much better than it being grey and rubbery.
Halve 1 avocado, remove pit, and thinly slice. Fan out slices.
Remove platter with lettuce from fridge. Arrange green beans, radish salad, avocado, and chicken separately on platter. Drizzle more dressing over and serve remaining dressing alongside.