Add the turmeric, chilli, coriander, cumin and garam masala powders. Cook over medium heat for a couple of minutes, stirring often, until the raw smell of the spices disappears. Add the mashed vegetables, salt and about quarter a cup of water. Cook for another 5 to 10 minutes until everything blends into a homogenous thick moist consistency with no gravy Mix in the chopped coriander and let it cool. Use to fill the Curry Buns.