Drizzle about 2 tablespoons of olive oil into a wide, deep saucepan. Add the sliced onion and cook on a gently heat, with the lid on for about 5 minutes, until softened but not brown.Add the ground cumin and coriander seeds and cook for 1 more minute with the lid off.Add the sweet potato, grated garlic and ginger, and cook for a further minute, before adding in 2 tablespoons of harissa, ½ teaspoon of salt, 1 tin of tomatoes and half a tin of water. Bring to the boil and then turn down low and simmer with the lid on for 10 minutes.While the tagine is simmering, you can start making the couscous (see recipe below).After 10 minutes, add the chickpeas and cook for a further 10 minutes with the lid off.When the tagine is cooked, add 3 tablespoons of roughly chopped coriander and the juice of half a lemon.Serve sprinkled with pomegranate seeds and coriander and with the Lemon and Coriander CouscousWhile the tagine is cooking, make the couscous. Place the couscous in a bowl and cover with the boiling water. Cover with a lid (I find a plate works well, or you could use tin foil) and leave for 5 minutes.After 5 minutes, fluff the couscous up with a fork and cover and leave for another 5 minutes.After the couscous has had 10 minutes in total, add the chopped coriander, juice and zest of 1 lemon, 4 tablespoons of olive oil, 50g of flaked almonds, plus salt and pepper to taste.