In a broad bowl, add the idli rice.
Wash and soak this for 3 hours.
If using sago, soak the sago also along with the rice.
Drain the water and add the chopped ash gourd and coconut to this.
Grind this into a fine paste.
Add water while grinding.
Take out and transfer to a bowl.
Let it be in the consistency of dosa batter.
Add salt and mix well with your hands.
Ferment this for 7 hours or overnight.
Mix the batter and take 1 and ¼ ladle of batter and pour on a hot dosa tawa.
Spread this into a dosa. Since the dosa will be soft, no need to spread this very thin.
Drizzle oil around the dosai.
Cover this with a lid and cook the dosa.
Once you see holes on the top, flip the dosa.
Cover and cook for 10 seconds.
Take it out from the tawa.
Ash gourd dosa is ready.
Serve with any spicy chutney of your choice.