Place chopped raw mango in a deep bowl, and set aside.

Splutter mustard seeds in hot oil in a deep pan. Lower the heat slightly, and fry garlic and ginger. Add in curry leaves and chopped green chillies. Lower the heat even further, and add ground turmeric, ground fenugreek, chilli powder, and asafetida. Let the spices fry for a while. Finally, add white vinegar, salt, and enough water to make the gravy. Turn up the heat, and let it come to boil. Remove from heat.

Now transfer the gravy to the bowl of chopped raw mangoes. Mix well. Pickle is ready. Once cooled, you can transfer it to a sterilized container.