1. In a bowl beat the yoghurt so that it is a smooth paste. Add the boiled and cubed potatoes, finely chopped red onion, coriander leaves, cumin powder, ginger, garlic and green chili paste, salt and stir it well to combine all the ingredients.
2. In a small pan with heated oil, crackle a couple of whole dry red chilies, mustard seeds and cumin seeds and pour this mixture over the top of the prepared yoghurt mixture to season it.
3. Serve chilled garnished with chopped coriander leaves and sprinkled with chopped red onion.