In a large dish, mix together the yogurt, harissa, garlic, thyme leaves and some seasoning. Add the lamb leg steaks and toss to coat in the sauce. Cover with cling film and leave to marinate for 10 minutes or overnight if time permits.
For the couscous salad, place the couscous into a large bowl, add the orange zest and a drizzle of olive oil. Pour over the hot stock (enough to cover by ½ cm), cover with cling film and leave for 4 minutes. Fluff up with a fork and then stir in the rest of the ingredients and season well.
Heat the olive oil in a large frying pan over a medium high heat, add the lamb steaks and fry for 3-4 minutes each side or until just cooked through but slightly pink in the middle. Remove from the pan and leave to rest.
To serve, thickly slice the lamb steaks and serve with the couscous salad and garnish with mint sprigs.
For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home and view the full Food safety at home video.