Combine all the seeds and grind them to a powder using a mixer grinder.
Transfer it to a bowl, add salt, mango powder, turmeric powder, red chilli powder, and asafoetida. Mix nicely. Taste, and if required, add more salt.
Add vinegar and mix the masala. It is now ready for stuffing the red chillies.
Start with cleaning and preparing red chillies for the pickle. Wash the red chillies and wipe them with a kitchen towel. Air dry the chillies to ensure they have no water after washing.
Wear kitchen gloves if your skin is sensitive to chilies. With a sharp knife, cut off the crown of the chilli and slit it lengthwise halfway through, leaving it intact from the lower end.
Scoop out white seeds and pith. Use a spoon for the purpose or wear gloves. Discard the seeds and white pith.
Stuff each red chilli with the pickle masala. Use your fingers to stuff the masala inside the chillies.
Once all red chillies are stuffed, transfer them to a sterilized jar. Make sure they are tightly packed in the jar.
Heat mustard oil in a pan. Once the oil starts smoking, turn off the heat. Allow it to cool down to room temperature.
Pour cooled-down mustard oil over the red chilli pickle.
Seal the jar with a muslin or other breathable cloth. Place it under the warm sun for 3 to 4 days. Daily, shift the pickle jar as per the sun’s rays during different hours of the day and bring it inside after sunset. Shake lal mirch ka achar two to three times during these 4 days.
After 3 days, you can check the red chilli pickle for doneness. If the skin of the red chillies has become thin, then the pickle is ready. Else, keep it under the sun for a few more days.
Store lal mirch ka achar for one year at room temperature.