Heat oil in a pan. Splutter mustard seeds and chana dal. Add the vermicelli and roast until golden brown. Transfer this into a bowl and keep it aside. In a bowl, mix together the yogurt, chopped green chilies, ginger paste, chopped coriander leaves, and salt along with the roasted vermicelli mixture. The batter should not be too runny or too thick. Leave it aside for 15 mins.

Grease the idli moulds with oil and pour a spoonful of the prepared batter into each mould. Place the moulds in the idli steamer and steam cook for 10-12 mins. Remove from flame and allow it to cool completely. Sprinkle some cold water over the idlis. Using a spoon, carefully scoop out the idlis without breaking them. Serve hot with chutney or as such.