Heat oil in a pan.
Add udad dal and saute.
Add the mustard seeds, chopped green chilly and curry leaves.
Add the finely chopped onion and cook for 3 to 5 minutes.
Add the onion mixture and salt to the idli batter and mix it well.
Heat the appam skillet (also known as appam patra or paniyaram pan).
Add a drop of oil in each of its grooves.
When the oil heats up, add a spoon full of the above batter in each of the paniyaram grooves.
Cover the skillet with a lid and let the appams cook for 3 to 5 minutes.
Flip the appams with the help of a spoon or knife and cook for another 2 minutes.
Serve hot with chutney.