For the koftas, peel and grate the bottle gourd. Squeeze to remove excess water.
Add the salt, gram flour, red chilli powder and mix well. Divide the mixture into twelve equal portions.
Stuff one piece of tamarind into each portion and shape them into round koftas.
Heat sufficient oil in a kadai and deep-fry the koftas, in small batches, for two to three minutes, or until golden brown and crisp on the outside.
Drain on absorbent paper and set aside. Heat three tablespoons oil in a non stick pan, add the onions and sauté until light golden brown.
Add the turmeric powder, coriander powder and red chilli powder. Continue to sauté on moderate heat for one minute, stirring continuously.
Add the tomato puree and two tablespoons water and continue to sauté till the oil surfaces.
Add two cups of water and bring to a boil. Add the salt, lower the heat and simmer for five minutes. Keep the gravy hot.
Add half the coriander leaves and mix well. While serving arrange the koftas on the serving plate, pour the gravy over them. Serve garnished with remaining coriander leaves.