Scrape the kankrol skin and discard the rough prickly parts. Cut them into half lenghtwise.
In a saucepan, boil some water and immerse the kankrols in them. Add a tbsp of salt and boil the kankrols for 5 to 6 minutes or until the kankrol has become soft enough for the seeds to be scooped out. It should not be too soft also.
Take them out and place them in a cold water bath to stop the cooking process.
Then using a spoon or a melon baller, scoope out the seeds and keep the seeds in a bowl.
Grind the seeds with green chilies, coconut, mustard seeds, salt and sugar. It need not be a very fine paste. A coarsely ground paste would also do.
Take the paste out in a bowl. Add finely chopped onion and mustard oil mix it well. Check the seasoning and adjust accordingly. The stuffing is ready.
Now fill the cavities of each half with the stuffing and arrange them on a plate.
Make a thin batter from the ingredients of the batter. Add a bit of salt to it as well. Add the water slowly. You might not need the entire 1/2 cup of water. A runny batter yet it should coat the kankrol is what you need.
Now heat oil in a frying pan. When the oil is hot, dip the kankrol in the batter and then slowly slide it in the hot oil. Repeat with all the kankrols.
Turn them when one side has become golden brown. Keep the heat at a medium or else it will burn.
When they have become a golden brown colour, take them out with a slotted spoon and place on a kitchen towel to soak the excess oil.
Serve kankroler pur bhaja as a side with rice and other accompaniments.
You can also have them as it is.