Thoroughly wash and clean the mangoes and cut into small pieces.
Add 2 tbsp salt and mix .Keep it aside for at least 2 hours, so that the mangoes pieces will be coated very well with salt and little water will come out from the mangoes .
Heat a heavy bottom pan and add oil into it.Splutter mustard seeds when oil heats up.Keep the flame to low and add curry leaves,(1/4 tsp fenugreek and ¼ tsp mustard) powdered mix,garlic and green chillies and saute.
Turn off the flame and add the powders(chilli powder,Kashmiri chilli powder,turmeric powder)and mix.
Keep the flame on low and saute till the raw smell vanishes completely.
Add asafoetida powder and fenugreek powder and saute on low flame.
Add vinegar.Adjust the vinegar according to the bitterness of the mango.
Add water(boiled and cooled ) and mix allow it to boil.
Turn off the flame and let it cool down for 5 mins.Add mango pieces into it.Check for salt.
Transfer the contents into a dry vessel.Spread gingelly oil (boiled and cooled) on top to avoid fungus.
Notes
Take slightly ripe mangoes(Little yellowish) Taste the skin of mango if it is bitter then remove the skin otherwise cut the mangoes along with the skin. Don't wash the mangoes after cutting. Cook on low flame.Keeping the flame on high may lead to burn the powders and may result in a bitter taste. Don't add tap water ,Always add boiled and cooled water. Don't turn on the flame after adding mangoes. Use only clean dry spoon to scoop the pickle from the jar. Do not use wet spoon which adds moisture and the pickle very easily get “fungus” and that spoils the whole pickle. Avoid using steel container for storing..Always store in dry ceramic jar / glass jar and please note to clean the bottle and caps you planning to use for pickle with hot water and wipe and dry well in sunlight without any water content.
Recipe by Kerala Cooking Recipes at https://www.keralacookingrecipes.com/mango-pickle-pacha-manga-achar/