Place all the marinade ingredients into a food processor or blender, and process until smooth. Place the lamb in a non-reactive dish, and coat evenly with the marinade. Marinate the lamb in the fridge for 3 hours.
Fill a large pot with cold water and add 2 tablespoons of salt. Add the potatoes, and bring to the boil. Cook for roughly 20 minutes or until tender. Drain and leave to dry. Reserve four cooked baby potatoes for the skordalia.
Make the skordalia by placing the reserved potatoes, garlic, juice, vinegar and water into a food processor or blender, blend until smooth. With the motor still running, slowly add the oil in a steady stream. Blend until well incorporated. Remove from blender and set aside until needed.
To prepare the Pulse for roasting over medium heat (210°C-240°C), preheat the barbecue by turning the control knob(s) to high. Preheat until the barbecue reaches at least 260°C, which will take approximately 15 to 20 minutes with the lid closed.
Once the barbecue is preheated, open the lid and brush the cooking grills clean. Adjust the control knob(s) to medium for roasting over medium heat.
Remove the lamb from the dish and discard the marinade. Place the lamb directly on the grill, skin side down. Cook for approximately 30 minutes, turning once, or until the lamb has reached your preferred internal temperature on your iGrill App. Remove from the barbecue and allow to rest for 15-20 minutes.
Lightly coat the potatoes with oil, salt and pepper. Cook the potatoes directly on the grill over medium heat for 15-20 minutes, or until golden and crispy, turning once. Slice the lamb and serve with the skordalia and potatoes.