Preheat the oven to 190°C/375°F/gas 5. Pound up your cumin, coriander and fennel seeds with the dried chillies, rosemary, ginger and a pinch of salt and pepper, stirring in a couple of tablespoons of olive oil. Smear half of this marinade over your lamb before you plait it. Rub and massage it in, then put the meat to one side while you mix the rest of the marinade in a bowl with the sweet potatoes, onions and garlic.
Brown your 4 marinaded pieces of meat on both sides in a pan with a little olive oil. Add the sweet potato mixture to the pan and remove the lamb to the empty bowl while you fry your veg for about 4 minutes until the onions are slightly soft. Add your tomatoes, give the pan a shake and place the meat on top. Add 3 wineglasses of water, the cinnamon stick, bay leaves and dried apricots, and braise in the preheated oven (I suggest you do this with the lid off to give it a little colour) for 1 hour 15 minutes. Now pour the boiling water over the couscous and allow it to be absorbed. Then fork the couscous through, season with salt, pepper, a lug of olive oil and a swig of wine vinegar, cover with tinfoil and place in the oven for 5 minutes to steam.
Roughly chop the fresh coriander and stir it through the stew just before serving. Divide between 4 plates with the couscous and spoon over a good dollop of natural yoghurt.