4 (6-ounce) skinless, boneless chicken breast halves 1/2 teaspoon salt, divided 1/4 teaspoon black pepper 1/4 cup all-purpose flour 3 tablespoons butter, divided 3 garlic cloves, thinly sliced 1 leek, trimmed, cut in half lengthwise, and thinly sliced (1 1/2 cups) 1/2 cup fat-free, lower-sodium chicken broth 2 tablespoons fresh lemon juice 2 tablespoons chopped fresh flat-leaf parsley