Heat the oil in a large saucepan and add mustard seeds. When they start to pop, add garlic, curry leaves and onion. Saute five minutes until onion is soft.
Add the green chillies, chilli powder, coriander and turmeric. Stir then add the tomatoes and spinach. Simmer 5 minutes.
Add the chickpeas and salt to taste. Simmer 1 minute to heat through. Stir in the yoghurt and serve.