Chop onions in a chopper. Chop green chillies.
Heat oil in a non stick pan, add mustard seeds and cumin seeds.
When they splutter, add curry leaves and onions and sauté. Cut each potato into 8 cubes.
When onions become golden, add ¼ cup water.
Add green chillies, potatoes, yogurt, kokum petals, salt and turmeric powder and mix well.
Chop coriander leaves. Add juice of lemon and mix well.
Add coconut and mix. Garnish with coriander leaves and serve hot.