Remove rack from non reactive dish and place on paper towels to dry off the marinade before you light the grill. Discard the remaining marinade. Place charcoal in a pyramid shape and light with either lighter fluid, electric starter or chimney starter. Wait until coals are gray and prepare the charcoal to the side for indirect heat method. Place rack on the grid.
Smoke roast for one hour to one hour ten minutes using a medium temperature.
Use the vents in the cover and on the grill to attain cooking temperature. Baste with the mustard sauce after twenty minutes on the grill and baste thereafter every twenty minutes until done. Do not overcook lamb. This marinade will really enhance lambs terrific flavor especially if you ask your butcher to provide you with Certified Fresh American lamb. That way you will not have to deal with the muttony taste and odor from the lamb of yesteryear.