Vatukappuli Naranga is bigger than the usual Lemon and has a thicker skin with a strong bitter taste to it.To reduce the bitterness put the naraga to hot water for few hours.
Slice the lemons and cut them in to small 1/4 size cubes. Slice the green chilly in to thin circles. Add the red chilly powder, roasted fenugreek powder, asafetida powder and enough salt to the sliced lemons and mix them together very well. Keep it aside for a couple of hours.
In a pan add 2 tbsp coconut oil and heat it up. Add 1 teaspoon mustard seeds to the oil and cover it with a dry lid to prevent splattering. When the seeds start to splutter add the broken pieces of dried red chilly, and the curry leaves. To this pour 1/2 cup water and heat it up until it boils. Add the lemon pieces and mix well and cook for few minutes. Taste and adjust the salt. Add vinegar if you want to store it for more days. Remove the pan from the stove and let it cool down. You can store this in a glass bottle when it is cold and keep it in the refrigerator.