Position an oven rack in the middle of the oven and heat the oven to 475°F. Season the lamb with salt and pepper. Combine the garlic, parsley, thyme, and breadcrumbs in a shallow bowl. Moisten the mixture with enough olive oil to make the mixture hold together.
Heat a large dry skillet over high heat. Put the lamb, meat side down, in the skillet. With tongs, hold the lamb against the skillet for a minute to give it a nice brown crust. Turn the meat to sear it on all sides for a total of 4 minutes. Remove the meat from the skillet and paint the meaty side of the rack with the mustard. Roll the meat in the herb mixture to coat it. Sear and coat the second rack in the same way.
Transfer the racks to a roasting pan just large enough to hold them. Cover the rib bones with strips of foil so they don't burn and roast until medium rare, 20 to 25 minutes (120°F internal temperature). If you want a crispier crust, finish cooking under the broiler for 2 minutes. Let the racks rest for 5 minutes before carving.
Use a carving knife to cut between the rib bones. Arrange the chops on warm serving plates. Serve hot. (The chops will cool quickly, so the best strategy is to carve the racks at the table.)