Grate the watermelon rind and squeeze out the excess juice.
In a mixing bowl, combine the grated watermelon rind, rice flour, grated coconut, cumin seeds, green chili, asafoetida, and salt.
Add enough water to make a thin batter. Mix well to remove any lumps.
Cover the bowl and let the batter rest for 4-5 hours or overnight.
Heat a non-stick tawa or griddle over medium heat.
Pour a ladleful of batter onto the tawa and spread it in a circular motion to form a thin dosa.
Drizzle oil around the edges of the dosa and cook until the underside turns golden brown and crispy.
Flip the dosa and cook for another minute or two.
Serve hot with chutney or any other accompaniment of your choice.