Clean with water and wipe the mangoes with a dry cloth. Chop them into one inch sized cubes.
Add the chopped pieces in a bowl with add turmeric powder and 5 tbsp of salt and mix it well.
Keep it in the sun for 4-5 hours covered with a sieve or a thin muslin cloth.
It will leave some water. So, drain that water and keep it aside.
Heat mustard oil to a smoking point and keep it aside. Let the oil cool down completely.
Roast fenugreek seeds, fennel seeds, mustard seeds, coriander seeds and cumin seeds on low flame for 2 minutes. Let it cool down completely.
Grind it to a coarse powder. Add asafoetida, red chili powder and more salt and mix well.
Add half the quantity of oil, chopped mangoes and spice mix and mix it well. Transfer the content in a pickle jar. Pour the remaining oil and mix well.
Keep the pickle in the sun for 5 days and at least mix it well once a day. The pickle will be ready to use after 8-10 days. Store it in a cool place and this pickle can be stored for up to 1 year.