Mix together besan, curd, water, turmeric, ginger paste, green chilly paste, salt and whisk them well. Place them in a saucepan and bring to a boil. Keep stirring till it thickens. Make it quite thick. Now remove it and spread the contents on to a thali or a marble/stone top and spread it very thin. Use the back of a knife or a pallet knife to spread evenly while it is still hot.
Heat oil in a pan, add mustard seeds, green chillies, and curry leaves, once it splutters add grated coconut and remove from heat. Add fresh coriander and mix and sprinkle this tempering on the khandvi. Reserve a little tempering for the garnish.
Let it cool completely. Run a knife on the spread khandvi in long strips 2” wide. Push the edges inwards and roll them up. Stack them and sprinkle with the remaining tempering and serve cold.