To make the spicy lamb, heat the oil in a heavy-based casserole and gently cook the onion for a few minutes until softened. Increase the heat and add the lamb, cooking until sealed. Add the dried spices and season well with salt and freshly ground black pepper. Cook for about 30 seconds before adding the chopped tomatoes and 200ml water. Bring to the simmer and cover with a lid. Cook gently for 1 hour, stirring a couple of times throughout.
After 1 hour, remove the lid and cook for a further 30 minutes until the lamb is tender. Scatter with coriander when serving.
To prepare the couscous, pour the very hot stock over the couscous in a large bowl. Add the olive oil, stir and cover with cling film. Leave for around 5 minutes by which time the stock will be absorbed into the couscous. Fluff the grains with a fork then stir in the olives, lemon and season.
Serve the couscous warm or at room temperature. If you want to prepare this well ahead of time, it can easily be heated through in the microwave. Scatter with the pomegranate seeds before serving with the hot lamb.