Wash the colocassia thoroughly and dry. Peel and make one slit on each of them without cutting through.
Mix the red chilli powder, coriander powder, turmeric powder, dried mango powder, garam masala powder and salt well. Stuff this mixture into the slits in the colocassia. Reserve the remaining masala.
Heat the oil in a pressure cooker, add the colocassia and sauté till lightly browned. Sprinkle the remaining masala and mix. Add half a cup of water and cook under pressure till the pressure is released once (one whistle is given out).
Open the lid when the pressure is reduced completely.
Garnish with the fresh coriander and serve hot.