Cut karelas through the centre but do not peel. Parboil these karelas along with salt, after boiling drain the excess water and keep it in sunlight for an hour.
In a bowl combine together karelas, turmeric powder, mustard seeds , salt and mix well Put the karelas in a vessel and again put this vessel in sunlight for one to two days.
Dry roast fennel seeds, fenugreek seeds and onion seeds in a non stick pand and saute till fragrant.Remove and grind to a coarse powder.
Add the ground powder, grated mango, red chilli powder, salt, asafoetida and oil in the karela mixture and mix well. Store it in the container for one week and serve.