Preheat the oven to 180°C. Combine the lemon zest and juice, 3 tablespoons olive oil, the F. Whitlock and Sons Smoky Manuka Style Rub and some freshly ground black pepper a small bowl. Place the lamb in a roasting pan, pour the mixture over then turn the lamb to coat evenly. Cover the lamb with foil and roast for 1 hour.
Meanwhile, place the potatoes in a large saucepan of salted cold water. Bring to the boil then cook over high heat for 4 minutes. Drain. Return potatoes to the saucepan with the extra 3 tablespoons olive oil, rosemary and paprika. Season with salt. Toss to combine. Set aside.
Remove the foil from the lamb. Add the potatoes to the pan. Stir to coat in cooking juices then return to the oven and cook, uncovered, for a further hour, turning potatoes occasionally.
Place the potatoes on a platter. Thinly slice lamb and place on top. Spoon pan juices over the lamb and serve.