Wash and soak chana dal for 3 to 4 hours.
Drain chana dal and transfer to a mixer jar.
Add green chilly and blend to a coarse paste without adding water. Keep this aside.
In a mixing bowl, add grated raw mango, ground chana dal, salt, sugar, grated coconut and chopped coriander. Mix well.
For the tempering. Heat 1 tsp oil in a small pan.
Add mustard seeds, hing, curry leaves and red chilly.
When they start spluttering, take off the heat and pour into the salad and mix well.
Refrigerate and serve chilled.