Soak chana dal in three cups of water for about one hour. Drain and boil with three cups of water, salt and turmeric powder till just done.
Heat a pan, add the boiled dal and half a cup of water if the dal is too dry. Stir and add half the red chilli powder, half the garam masala powder, dry mango powder and adjust salt. Stir gently and cook on low heat.
Heat oil in another pan and add cumin seeds. When they begin to change colour, add green chillies, curry leaves, remaining garam masala powder, remaining red chilli powder. Stir and add it to the dal. Mix well and take it off the heat.
Garnish with onion and coriander leaves and serve hot.