Chop the mangoes into small pieces and keep aside. Take a large bowl, add chopped mangoes along with chilli powder, turmeric powder and salt, mix well and adjust the spice according to your taste by increasing or decreasing the chilli powder.
Cover the bowl and keep aside for 10-15 minutes (this is optional).
Dry roast fenugreek and mustard seeds, allow them to cool and then grind into a fine powder.
Add this grounded powder to the pickle and mix well.
Heat a pan with oil, add asafoetida and mustard seeds, when the mustard seeds begin to crackle add this to the pickle and stir well.
Allow it to sit for at least 10 minutes so that all the spices are nicely blended with mangoes.
Always use dry spoon when using and keep refrigerated for long shelf life.