Take green chilli and ginger in a blender and puree till smooth.
Take yogurt, gram flour, the puree and whisk well. Add water and whisk well.
Heat oil in a kadai. Add all seasoning ingredients and let it sizzle. Add in yogurt mix and bring it to a boil. Boil it for 2 to 3 mins. Add in salt, sugar and mix well. Add in coriander leaves and mix well. Serve.