Combine the breadcrumbs, mint, parsley, and garlic in a small mixing bowl.
Preheat the oven to 450°F. Heat an ovenproof skillet large enough to hold both racks of lamb until hot over medium-high heat. If you do not have a skillet large enough for both racks, then place a roasting pan in the oven to heat as the oven preheats.
Season the lamb generously with salt and pepper on all sides. Spray pan generously with cooking spray. Place one rack of lamb in the skillet and cook for 2 minutes per side or until browned. Remove the rack from the pan and repeat with the other rack.
Brush the lamb with the mustard and press the breadcrumb mixture over the lamb.
Place both lamb racks back in the pan and roast in the oven for 18 minutes or until an instant-read thermometer inserted into the thickest part of the lamb reaches 130°F. Let sit for 10 minutes before cutting and serving.