Slow cooker Moroccan lamb stew

Name: Slow cooker Moroccan lamb stew
Ingredients: 2 tbsp olive oil or rapeseed oil; 1kg diced lamb shoulder; 2 onions halved and sliced; 5 garlic cloves crushed; thumb-sized piece ginger peeled and grated or finely chopped; 1 tbsp ground cumin; 1 tbsp ground coriander; 1 tsp ground cinnamon; pinch saffron (or turmeric, to add colour); ½ large or 1 small preserved lemon skin only, finely chopped; 1 tbsp tomato purée; 600ml hot beef stock or lamb stock; 1 tbsp honey; 1 lemon zested, plus a squeeze of juice; 80g pitted Kalamata olives; handful chopped mint coriander or parsley (or a combination); couscous or rice, to serve