How to Make It
Preheat the oven to 325°. In a bowl, mix the bread crumbs with the butter, garlic, parsley, thyme, rosemary and lemon juice. Season the lamb all over with salt and pepper. Rub some of the herb mixture on the underside of the lamb and set in a roasting pan, fat side up. Spread the mustard over the top of the lamb, then pat the remaining herb mixture over the top of the lamb.
Bake the lamb for about 2 hours, until browned on top and an instant-read thermometer inserted in the thickest part of the meat registers 150° for medium meat.
Transfer the lamb to a carving board and let rest for 15 minutes. Carve into slices and serve.