Pre heat your oven to 250 degrees (I used a Big Green Egg BBQ in the show)
Make cuts across the surface of the leg of lamb in a crisscross fashion about 1cm deep.
Combine the harissa paste, yoghurt and lemon juice in a small bowl. Season with salt if required. Smear the paste all over the cut leg of lamb and then sprinkle with the crushed coriander seeds.
Place the lamb leg on a roasting rack over a tray and place inside the hot oven and cook for 45 minutes on high heat.
While the lamb is cooking, heat the oil in a wok and fry the eggplant chunks until golden and soft, then remove and drain. Repeat the process until all the eggplant is cooked. Remove all but 3 tablespoons of oil from the wok and reheat.
Add the sliced onions and season with a teaspoon of salt. Fry for 5 minutes until soft and starting to brown.
Add the spices and pureed garlic and ginger and fry for a further 2-3 minutes.
Add the diced tomatoes and combine. Then add the drained eggplant and fold together. Turn of the heat and season with vinegar, salt and pepper. Then add the chopped herbs and leave to settle.
When the lamb is cooked allow to rest for 15 minutes and then serve whole with the eggplant brinjal.