Lamb chickpea spinach curry with masala mash

Name: Lamb, chickpea & spinach curry with masala mash
Ingredients: 1 tbsp oil; 500g lean lamb stewing cubes; 1 red onion, sliced into half moons; 1 cm piece ginger, peeled and finely chopped; 2 garlic cloves, crushed; 1 tbsp ground cumin; 1 tbsp ground coriander; 400g can tomato; 200g can chickpeas, washed and drained; 1 tsp garam masala; 100g spinach, roughly chopped; 700g potato, peeled and quartered; 1 tbsp korma curry paste (we used Patak's); 100ml thick yogurt