Mix the buttermilk with water.
Combine the besan, butter milk water mixture, lemon juice, ginger-green chilli paste, turmeric powder, asafoetida and salt in a deep non-stick pan and mix well to make a smooth batter (taking care that no lump remains).

Cook on a slow flame, while stirring continuously till it becomes thick (approx. 8 to 10 minutes).
Grease a thali on tthe back side using ¼ tsp of oil and spread a spoonful of the batter on a greased thali and wait for a few seconds and try to roll up. If it doesn’t, then cook for a few more minutes, and check once more time till done.

Divide the batter into two equal portions. While the batter is still hot, spread each portion evenly using a spatula, on the reverse greased side of 2 thalis evenly to make a thin layer using a spatula.

When cool, cut the khandvi on each thali lengthwise into equal portions and roll up each properly.

For the tempering, just before serving heat the remaining 3 tsp oil in a small non-stick pan and add the mustard seeds.
When the seeds crackle, add the asafoetida, curry leaves and green chillies and sauté on a medium flame for a few seconds.

Pour the tempering over the khandvis.
Serve immediately garnished with coconut and coriander.