Fennel Gratin with Pecorino and Lemon

Name: Fennel Gratin with Pecorino and Lemon
Ingredients: 5 tablespoons olive oil; 1 12- to 13-ounce onion, halved, cut into 1/4-inch-thick slices; 3 large garlic cloves, minced; 5 large fresh fennel bulbs, trimmed, cored, cut into 1/4-inch-thick slices; 1/2 cup low-salt chicken broth; 2 tablespoons chopped fresh Italian parsley; 1 tablespoon chopped fresh thyme; 1 1/2 teaspoons coarse kosher salt; 1/2 teaspoon black pepper; 3 tablespoons butter; 3/4 cup panko (Japanese breadcrumbs); 1 cup Pecorino Romano cheese; 1 tablespoon chopped fresh Italian parsley; 1 1/2 teaspoons finely grated lemon peel