Slow cooker curried lamb with lentils

Name: Slow cooker curried lamb with lentils
Ingredients: 500 g (1lb 2oz) lean stewing lamb on the bone, cut into 8 pieces (ask your butcher to do this), fat trimmed; 1 tsp. ground cumin; 1 tsp. ground turmeric; 2 garlic cloves, crushed; 1 medium red chilli, deseeded and finely chopped; 2 1/2 cm (1in) piece fresh root ginger, peeled and grated; 2 tbsp. vegetable oil; 1 onion, finely chopped; 400 g tin chopped tomatoes; 2 tbsp. vinegar; 175 g (6oz) red lentils, rinsed; Large handful fresh coriander leaves, to garnish