In a pan, heat oil. Once it is hot, add mustard seeds, urad dal and channa dal. Fry until the ingredients are golden brown.
Add thinly sliced green chillies and finely chopped ginger. Add a pinch of asafoetida and quickly mix it without burning the asafoetida.
Now, add finely chopper onion and roughly chopped curry leaves.
Add salt to taste. Idly /dosa batter has already salt in it. so add salt just needed for the onion. if you are using store bought idly batter, taste the batter and adjust the salt accordingly.
Saute the onion till it becomes soft.
Towards the end, add the coriander leaves and give nice stir. keep aside and prepare the batter.
Take 3 cups of idly/dosa batter in a bowl.If it is very thick, dilute it with 2 to 3 tbsp of water, mix well and set aside. Add the sauteed onion to the batter. Mix well.
Heat the paniyaram pan. Fill 1/4 tsp oil in each mould of the paniyaram pan.
Add a ladle of battter to it and cook covered for 2 minutes.
After 2 minutes, open the lid and flip the paniyarams to cook its other side using a skewer or spoon or fork.
Once the other side is cooked, transfer the paniyarams to a plate. Insert a skewer into a paniyaram and check if it comes out clean. If it comes clean, then the paniyaram cooked well.
Serve hot with any spicy chutney. Repeat the step with the remaining batter.