Wash green chillies, wipe them with a dry cloth and keep them for a while, preferably overnight, so that moisture if any, goes off.
In a pan, dry roast Rai (Mustard Seeds), Methi Dana (Fenugreek Seeds), Saunf (Fennel Seeds) and Kalonji (Onion Seeds) for 3 to 4 minutes till you can start smelling the lovely aroma of these spices.
Let them cool down completely. Till the spices are resting to cool down, you prepare the chillies.
Make a slit in the chillies, ensuring that they remain intact. And take out all the seeds from within. Do not use your hands to remove the seeds as they will leave your hands burning. Always use a spoon or fork to remove the seeds.
Keep them aside.
When the roasted spices are cool, grind them coarsely.
Add salt, dried mango powder (amchoor), turmeric and asafoetida.
Add 1 tablespoon mustard oil and 1 tablespoon lemon juice and mix it nicely. Your spice mix is ready. Now, this mixture can be used in 2 different ways. First is to make this pickle only. And the other is to make instant green chilli pickle.
Fill this mixture in the hollowed green chillies.
Take a glass jar, ensure that it is completely dry, and put the chillies in it.
Now, a very important step. After filling the chillies in the jar, put 1 tablespoon mustard oil and juice of 3 to 4 lemons on it. This is done to protect the outer covering (skin) of the chillies.
Shake the jar slightly and keep it in some warm place for a week or so. Do not forget to shake the jar daily until the pickle is ready.