Cut potato/kadachakka into small cubes/pieces. Heat oil, fry mustard seeds, add onion, green chilli & curry leaves, stir until it turns light brown. Then add salt, all the powders and masala, stir until it turns brown, then add coconut milk and veg., stir well, cover it and cook until well cooked. (If not adding coconut milk, add a cup of water instead). It is ready to serve! (Infact, it should be made by roasting coconut and all the spices, and blending them very nicely, but it is not easy to do it here. So I made up this version.) (You can cook kadala too the same way. For kadala, you can use just the garam masala and chilli powder only. Either way, it tastes good.)