Preheat oven to 200°C (180° fan-forced). Place lamb racks in the centre of a baking tray lined with baking paper. Brush the lamb rack with 1 tablespoon oil, sprinkle with sumac, season and cook lamb for 25-30 minutes or until cooked to your liking. Remove from oven, place lamb on a plate loosely covered with foil and rest for 5 minutes.
Meanwhile, line a large baking tray with baking paper. Spread onion, zucchini, capsicum, sweet potato and brussels sprouts onto tray, season, drizzle with 1 tablespoon oil and toss to coat. Cook vegetables for 25-30 minutes or until golden and tender.
Cook couscous according to packet instructions. Drain well. Place in a large bowl with roasted vegetables, season and toss well to coat.
In a small bowl combine remaining oil, garlic, parsley, lemon zest and juice. Season and stir. In a separate bowl combine yoghurt and coriander. Season and stir.
Slice lamb racks into individual cutlets and serve with couscous salad, gremolata and coriander yoghurt. Garnish with extra parsley leaves.
Lamb rump, leg steaks or cutlets would also work well in this recipe.
Swap the sumac for any other spice of your choice.
Make sure you rest the lamb to maximise tenderness and lock in the juices – for 4-cutlet racks rest for 5 minutes.