Spread salt on the mango slices and leave it for two days, shaking once a day.Separate the watery liquid and the mango pieces into two different vessels.Spread the mango pieces on a large plate and dry it in the sun for one full day.Heat 2 tsp of oil in a fry pan, add mustard seeds.When it pops, add fenugreek seed powder, asafoetida and then add red chilli powder.Add the preserved watery juice to this and bring to boil.Now add the mango pieces and cook for 2 min.Now add the remaining oil and stir well.Allow the pickle to cool to room temperature and store in glass bottles.