Stuffed aubergine with lamb and pine nuts

Name: Stuffed aubergine with lamb and pine nuts
Ingredients: 4 medium aubergines (about 1.2kg/2lb 7oz), halved lengthways; 6 tbsp olive oil; 1½ tsp ground cumin; 1½ tbsp sweet paprika; 1 tbsp ground cinnamon; 2 medium onions (340g/12oz in total), finely chopped; 500g/1lb 2oz lamb mince; 50g/1¾oz pine nuts; 20g/¾oz flatleaf parsley, chopped; 2 tsp tomato purée; 1 tbsp caster sugar; 1½ tbsp lemon juice; 1 tsp tamarind paste; 4 cinnamon sticks; salt and freshly ground black pepper; 1 loaf sourdough, to serve (optional); 125g/4½oz natural yoghurt; 50g/1¾oz tahini; 1 garlic clove, finely chopped; 2 tsp lemon juice; 1 small bunch coriander, chopped