Prawns with Tomato, Preserved Lemon and Couscous

Ingredients

• 40 ml olive oil
• 1 Spanish onion, thinly sliced
• 2 baby fennel bulbs, thinly sliced
• 2 garlic cloves, thinly sliced
• 1 tsp each ground cumin and ground coriander
• ½ tsp ground chilli
• 400 gm canned cherry tomatoes
• 500 ml (2 cups) vegetable stock
• 320 gm (2 cups) instant couscous
• 30 gm butter, coarsely chopped
• 2 lemons, juice only (or to taste)
• 20 medium green prawns, peeled and cleaned
• 2 tbsp finely chopped preserved lemon rind
• To serve: thick natural yoghurt and coarsely chopped mint and flat-leaf parsley