Wash the green chillies thoroughly & remove stems from them.Pat the chillies dry in paper towel and make sure all moisture is removed from them.This is absolutely necessary else the pickle will turn bad.
Using a sharp knife , make a lengthwise slit in all the chillies but not all through. Next remove/scoop all the seeds and veins from inside of the chillies.Reserve these to be used for making the stuffing.[You can use round tip of your peeler to do so]
In a small bowl, add all the spices to the scooped veins & seeds and mix well to make a masala .Next, stuff all the green chillies with the this masala .You will have some left over masala.Dont throw it.
Now, I like to cut the stuffed chillies into 2-3 pieces.You can keep them whole if you like it that way.
In a dry glass container with a tight lid, put the cut stuffed green chillies.Tip in the leftover masala into the container.Next, pour mustard oil into container till the chillies are just covered.
Now keep this glass container in a dry, sunny place for around 1-2 days till the chillies become pale green and soft!
Pickle is ready to eat.Serve with stuffed parathas, pooris [indian flatbreads] or relish it with dal -rice.
Absolutely make sure that the chillies & container are moisture free.
There is no need of putting the pickle in refrigerator.It can lead to increased moisture in the pickle.Sun-cooked pickles normally last at room conditions for months together.
If you do not want your pickle to be very hot, do not not add the scooped veins & seeds from the green chillies.