1) Wash the bitter gourds thoroughly with warm water. If the bitter gourds are of longer variety, cut them into pieces of 3 inches. Remove skin from bitter gourds by scraping with a sharp knife. Set the skin aside.
2) Slit the bitter gourds lengthwise. Remove the seeds and mix seeds with the skin scrape.
3) Take 1 teaspoon of salt and apply it thoroughly to all of the bitter gourd pieces; set aside for about 1 hour. Also mix 1 teaspoon of salt to the bitter gourd skin and set aside for 1 hour.
4) Heat a non sticking frying pan and add 2 teaspoons of oil. When the oil becomes hot, add the cumin seeds and asafoetida. When the seeds turn dark, add the onion, green chillies, ginger and garlic. Saute for about 3 minutes then add in the gram flour, chilli powder, salt, coriander powder, turmeric powder and mango powder. Stir well and fry until the mixture turns light brown, for about 5-7 minutes.
5) Add half of the coriander leaves and mix. Take the bitter gourd skin in a sieve and wash it thoroughly with warm water. Add it to the washed skin scrape mixture and stir.
6) Wash the bitter gourds well with water. Fill the above mixture in each bitter gourd. Heat a non sticking frying pan and add oil. Place all of the bitter gourds in the pan, cover with lid and reduce heat to low. Let bitter gourds cook covered for about 7 minutes. Turn each bitter gourd over and cook other side, covered for another 7 minutes. Finally sprinkle the other half of coriander leaves.