Heat the oil in a saucepan and add the mustard seeds. When they start to pop, add the garlic, curry leaves and onion. Cook over a moderate heat for 5 minutes or until the onion is soft.
Add the green chillies, chilli powder, coriander and turmeric. Mix well, then add the tomato pieces. Give a nice stir, then add the spinach. Cook over a low heat for 5 minutes.
Now add the black eyed beans with salt to taste. Cook for a further 1 minute until everything is hot. Remove the pan from the heat and slowly add the yoghurt, stirring well. Serve warm with plain rice or chappati.