Harissa prawn skewers with carroty couscous

INGREDIENTS

• 1 tbsp olive oil
• 1½ tsp cumin seeds
• 3 carrots , coarsely grated
• 200g couscous
• 400g raw prawns
• 16 cherry tomatoes
• 1 onion , cut into 12 thin wedges, leaving root intact
• 1 tbsp harissa
• 2 tsp tahini paste
• 2 tbsp low-fat natural yogurt
• 1 small garlic clove , crushed
• juice ½ lemon , plus wedges, to serve
• handful mint leaves, roughly chopped