In a large bowl, combine bread crumbs, garlic, rosemary, 1 teaspoon salt and 1/4 teaspoon pepper. Toss in 2 tablespoons olive oil to moisten mixture. Set aside. Season the rack all over with salt and pepper. Heat 2 tablespoons olive oil in a large heavy oven proof skillet over high heat. Sear rack of lamb for 1 to 2 minutes on all sides. Set aside for a few minutes. Brush rack of lamb with the mustard. Roll in the bread crumb mixture until evenly coated.
For the lamb, place the lamb steak into a bowl, rub with the olive oil and season with salt and freshly ground black pepper. Heat a griddle pan and chargrill the steak for 5-6 minutes on each side, or until cooked to your liking. Leave to rest for five minutes.
Broil the steak for 8 to 12 minutes, turning once. Put the broiler pan on the top rack of the oven and cook the steak four to six minutes on each side. A London broil that goes for 8 minutes will cook to rare, while a steak that cooks for 10 minutes will cook to medium-rare to rare.