Chilled Zucchini Soup with Chicken

Name: Chilled Zucchini Soup with Chicken
Ingredients: 6 tablespoons extra-virgin olive oil; 2 leeks (white and light green parts), halved lengthwise and cut into half-moons; Kosher salt; 1 1/2 pounds zucchini (2 to 3 medium), chopped; 2 bay leaves (preferably fresh); Freshly ground pepper; 1/2 cup buttermilk; 1 cup fresh dill, plus 2 tablespoons chopped; 1/2 cup fresh parsley, plus 2 tablespoons chopped; 2 heaping cups cubed crusty white bread; 2 cups shredded rotisserie chicken, skin removed; 1/2 teaspoon finely grated lemon zest, plus 1 tablespoon juice; 1 tablespoon whole-grain mustard