Soak the par-boiled rice in hot water for 2 hours. Now grind pumpkin pieces, coconut, red chilies, tamarind paste, asafoetida, salt and jaggery together into a thick paste in a mixie without adding water.
Now strain the rice and grind it along with the above paste using grinder into a thick and smooth batter. Do not add water at all. Once done transfer the batter to a bowl lined with a thick cloth. Now tie the cloth and keep it aside for 15 min till the cloth absorbs all the moisture from the batter. Add a spn of oil in a pan and splutter mustard seeds. Add this to the above batter along with finely chopped curry leaves and mix well.
Now roll lemon sized balls from the batter and press in between two greased plastic sheets to make a flat round of 3mm thickness. Make a hole in the center with your finger. Gradually remove it from the sheet and deep fry it oil, roasting it on both sides. Do not over roast. The vadai should be really soft. Now place them on tissue to remove excess oil. Serve it hot with raw onions.