Wash mangoes thoroughly and wipe with a cloth. Set aside for an hour to dry.
Cut the mango along with the seed into medium size.
Clean the pieces with a soft cloth and spread them over a dry cloth.
Take a huge bowl which fits all the mangoes along with other ingredients.
Place the mango pieces in the bowl. Add red chilli powder, mustard powder, salt, turmeric powder, fenugreek powder and crushed garlic. Mix thoroughly with the mango pieces.
Finally add gingelly oil and mix thoroughly.
Transfer the pickle into the pickle jar. Make sure the pickle jar is dry and there in no hint of moisture or wetness. The pickle is not ready yet to consume.
Keep the jar aside for 3 days. On the third day, mix the pickle thoroughly and add little more oil if needed.
The mango pieces will remain raw and hard in the initial days and will become soft after a month. This pickle can be stored for a year.
Serve the pickle with hot rice and ghee. It also goes well with idli, dosa or roti.