Peel and grate the bottle gourd. If you have a steamer, steam the lauki along with green chilli and raisins. If not then boil in water till done and then drain out the water. Set aside for cooling.
Whisk the curd till smooth. Add the steamed/boiled lauki and salt.
In a small pan, heat mustard oil. Add panch phoran and sautee for 2 minutes till fragrant. Add to the raita and serve chilled.
Panch Phoran is a bengali spice mix made of five spices mixed in equal amounts. The spices are fenugreek (methi dana), nigella seeds (kalonji), cumin seeds (jeera), fennel seeds (saunf) and mustard seeds (rai).