Scrub and rinse the mango well. Peel off a small piece of the skin and taste it. If it tastes fine, you don't need to peel it before pickling. Only, if it has an off or bitter taste, do you need to peel the mango.. Chop the mango into small pieces. Peel the small garlic cloves(4heaped Tbsp) and leave them whole, or slice lengthwise into smaller pieces if you have the larger cloves.. Heat the oil(3Tbsp) in a heavy-based pan or wok. Add the fenugreek seeds(1/2tsp) and as soon as they splutter, switch off the heat.. Add the green chillies, garlic and stir in the residual heat till they are just slightly tenderized in the hot oil.. Add the Kashmiri chilli powder(1 1/2Tbsp), along with the asafoetida(1 1/2tsp) and stir well, till fragrant.. Add the vinegar(3/4-1cup) and then turn the heat back on. Bring to a boil and simmer for a minute or so.. Once this mixture starts to thicken a bit, turn off the heat once more and allow it to cool off  - till lukewarm.. At this stage, add the chopped mango and the yellow mustard seeds.. Once cooled off completely, store in a sterilized - dry jar.  Approx 1 1/2 cups..