Tandoori lamb wrap

Name: Tandoori lamb wrap
Ingredients: 150ml/5fl oz Greek-style yoghurt; ½ small onion, roughly chopped; 1 garlic clove, peeled and chopped; 2.5cm/1in piece fresh ginger, peeled and chopped; 2 tsp each garam masala and ground cumin; 1 tsp ground coriander; ½ tsp ground fennel seeds; ¼ tsp freshly ground black pepper; 1 tbsp vegetable oil; 2 tbsp fresh coriander leaves; ½ tsp red chilli powder, or to taste; 2 tsp lemon juice; 1 tsp salt, or to taste; 400g/14oz lamb (leg meat is ideal), bones removed, cut into 2cm/1in cubes and pierced with a fork; 2 tbsp melted butter, for basting; 5 ready-made flour tortillas, wrapped in foil and placed in the oven for the last five minutes of cooking; ½ onion, finely sliced; 2 tomatoes, finely sliced; 1 Little Gem lettuce, finely sliced; 100ml/3½fl oz green chutney , mixed with 3 tbsp yoghurt, to serve; You'll need ten wooden skewers, soaked in water for half an hour