Heat the ground nut oil in a tagine and gently cook the onion and garlic until soft.
Add the cumin, ginger, cinnamon stick, preserved lemon and green olives and cook for two minutes.
To make the harrissa put the chillies, garlic, lemon juice and olive oil into a food processor and blend into a rough paste.
Stir in the harrissa and cook for one minute.
Add the wine and fish stock and the saffron and bring to a gentle simmer.
Add the fish and cook for a couple of minutes, then add the mussels and cherry tomatoes, season with salt and pepper and cover. Cook gently for 6-7 minutes.
Serve on a bed of steamed couscous and sprinkle with freshly chopped coriander.
