Heat oil/ghee in a pan and crackle mustard and urad dal. Add sliced small onion, chopped ginger, green chilli and coconut. Fry it till the onion turns golden brown.
Add the fried items and chopped coriander leaves to the idli batter and mix well.
Heat oil in Paniyaram/Unniyappam pan. Make sure the oil is hot, but not smoking hot. Drop spoonfuls of the batter into hot oil and deep fry till golden brown. Flip the paniyaram, once, to cook both sides.