Place the chicken thighs in the bottom of the slow cooker insert.
Heat a fry pan over a medium heat.
Add the olive oil and onion, and fry for 5 minutes or until the onion is golden brown.
Stir in the garlic and ras el hanout.
Fry for 1 minute, or until you can smell the garlic and spice mix.
Pour the onion mixture over the chicken thighs.
Add the chicken stock to the fry pan, and gently heat for 1 minute to deglaze the pan.
Pour the chicken stock into the slow cooker.
Add the chickpeas, preserved lemon, saffron and olives.
Finely chop the bunch of coriander (cilantro), including the roots and stems. Reserve the leaves, and add the chopped roots and stems to the slow cooker.
Season with salt and pepper.
Gently stir to coat the chicken and evenly distribute the ingredients.
Cook on High for 4 hours or Low for 8.
Stir through the reserved chopped coriander leaves, and serve with wholegrain cous cous.