Grilled aubergines with spicy chickpeas & walnut sauce

INGREDIENTS

• 4 tbsp olive oil
• 1 onion , finely chopped
• 1 red chilli , deseeded and finely chopped
• 2cm piece ginger , finely chopped
• ½ tsp each ground cumin , coriander and cinnamon
• 400g can chickpeas , rinsed and drained
• 200g tomatoes , chopped
• juice ½ lemon
• 2 aubergines , sliced lengthways
• 200g tub Greek-style yogurt
• 1 garlic clove , crushed
• 25g walnuts , chopped
• handful coriander leaves, roughly chopped