Preheat the grill to 375°F or 190°C making sure you have space for both racks of lamb to cook with indirect heat.
In a small bowl combine all ingredients except for the lamb. Using a brush cover all sides of the lamb with the oil mixture.
Once the grill is hot place the meat side down on the grill and cook for 5 minutes undisturbed. Then move to the side of the grill with indirect heat and cook for another 15-20 minutes or until internal temperature reaches 120°F or 49°C.
Remove from the grill and allow to rest for 10-15 minutes before slicing.