Lightly toast the fenugreek seeds until fragrant. Let it cool and then pound roughly in a mortar pestle.
In a bowl, combine the grated raw mango, kashmiri red chilli powder, turmeric powder, toasted fenugreek powder and add the salt. Start with 2 teaspoons and mix thoroughly Taste and adjust/add more depending on sourness of the mangoes. Set aside atleast 15-20 minutes.
Heat the sesame/neutral oil in a pan. When hot, add the mustard seeds and let them splutter. Add the smashed garlic clove and let it frizzle and start to change colour without browning. Turn off the heat and add the asafoetida and curry leaves. Let it cool.
To the spiced grated raw mango mixture, add the cooled oil tempering and mix well. Ladle the pickle into clean jars. The pickle lasts for upto a week in the refrigerator.