Grape and Grain Salad with Lemony Chicken

Name: Grape and Grain Salad with Lemony Chicken
Ingredients: 1/2 cup olive oil; 1/2 cup sliced fresh mint; 1 tablespoon honey; 1 tablespoon Dijon mustard; 2 lemons, zested and juiced; 1/2 medium shallot, finely chopped; Kosher salt and freshly ground black pepper; 4 boneless skinless chicken breasts (6 to 8 ounces each); 1 3/4 cups low-sodium chicken broth; 1 cup quick-cooking barley; 1 1/2 cups mixed red and green seedless grapes, halved; 1/4 cup chopped walnuts; 2 radishes, halved and thinly sliced; 1 stalk celery, thinly sliced