In a medium bowl, whisk the yoghurt and 1 tbs of the oil with garlic, cumin, coriander, turmeric, 1 tsp sea salt flakes and ½ tsp freshly ground black pepper. Add the lamb and turn to coat. Set aside for 30 mins to marinate.
Prepare a barbecue for medium-high heat. In a medium bowl, whisk the lemon rind, ⅓ cup (80ml) lemon juice, ⅓ cup (80ml) oil, chopped parsley, ¾ tsp salt and ¼ tsp pepper.
Remove the lamb from the marinade and wipe off the excess. Barbecue the lamb for 5-6 mins each side or until browned on both sides and internal temperature is 54°C for medium-rare doneness. Transfer the lamb to a serving platter. Spoon half the lemon juice mixture over the lamb and set aside for 5 mins to rest.
While the lamb is resting, combine asparagus, spring onions and remaining 1 tbs of oil in a bowl. Season with salt and pepper. Barbecue the asparagus mixture, turning occasionally, for 4 mins or until the asparagus and spring onions are charred all over and asparagus is just tender.
Transfer the asparagus mixture to the serving platter with the lamb. Drizzle with remaining dressing. Top with the radish and parsley sprigs. Serve with the lemon wedges.