Italian Springtime Lamb

Name: Italian Springtime Lamb
Ingredients: One 5-pound trimmed and boned leg of lamb, butterflied; 3 tablespoons olive oil; 6 cloves garlic, minced; 4 sprigs fresh rosemary, leaves removed and chopped; 1/4 teaspoon red pepper flakes; 1/2 cup chopped walnuts; One 5-ounce container baby spinach leaves, roughly chopped; 1 1/2 teaspoons kosher salt; 3/4 cup raisins; 1/2 teaspoon freshly ground black pepper; 1/2 cup whole-grain mustard; 1 tablespoon extra-virgin olive oil; 1/3 cup panko breadcrumbs; 1/3 cup coarsely chopped fresh Italian parsley; 1 teaspoon grated lemon zest (from 1 large lemon); 1/8 teaspoon kosher salt