Preheat the oven to 220°C. Place a heavy, rimmed baking tray on the bottom rack of the oven.
In a large bowl, toss the potatoes with 2 tbs of the oil and season with salt and pepper. Transfer the potatoes to the preheated baking tray and roast for 30 mins or until potatoes are tender inside and crisp on the outside. Using the back of a wide wooden spoon, lightly smash the potatoes so that they are compacted but not broken. Transfer the potatoes to a 25cm x 25cm x 5cm baking dish.
Meanwhile, season the lamb with salt and pepper. Heat a large, heavy frying pan over medium-high heat. Add 2 tbs of oil, then add the lamb and cook, turning occasionally, for 6 mins or until the lamb is golden brown all over. Set the lamb racks fat side up on another baking tray. Roast the lamb for 18 mins or until a meat thermometer inserted into the thickest part of the meat reads 55°C for medium-rare doneness. Transfer the lamb racks to a carving board and rest for 5 mins.
In a small bowl, mix the parsley, mint, oregano, lemon zest, 1 tbs of lemon juice, shallot, chilli flakes and the remaining 6 tbs of oil. Season the sauce to taste with salt and pepper.
Preheat the grill. In a small bowl, combine the haloumi and cream. Spoon the cheese mixture over the roasted potatoes. Grill the potatoes for 2-4 mins or until the cheese has browned and slightly melted.
To serve, cut the lamb into 8 double chops. Place 2 double chops on each of 4 plates and spoon some of the sauce over the lamb. Serve with the warm haloumi potatoes.