Place the potatoes and onions into a slow cooker and season with salt and freshly ground black pepper. Season the chicken generously. Heat the vegetable oil in a large frying pan then fry the chicken until golden-brown all over, about five minutes each side. Put the chicken on top of the vegetables.
Meanwhile, finely grate the zest of the lemon, cut four thin slices of lemon, then squeeze the juice from the rest of the fruit. Add the zest, garlic and ras el hanout to the chicken fat and juices, fry for a one minute till fragrant, then pour in the lemon juice and stock. Bring to the boil, then pour over the chicken. Top with the lemon slices, olives and one tablespoon olive oil from their jar, then cover with the lid and cook on low for six hours, until the chicken is very tender.
To serve, drizzle with the honey. Roughly chop the parsley leaves and scatter over the chicken. Serve with dollops of creamy yoghurt.