Soak the chana dal for 2 hours in warm water. Rinse and grind dal with ginger and green chilli to a coarse paste.
Grate potatoes and mix with the dal paste. Add salt to taste.
Grease a wide vessel which you're going to make the kalmi vadas in. Heat water in a bigger vessel for steaming.
Add the Eno salt to the dal batter and mix well. Transfer the batter to the greased vessel and steam it on a low-medium flame for 20 minutes.
Once the steamed mix cools down, cut it into rectangular pieces and store it in the refrigerator till it's time to fry. You can store it for up to two days like this.
When it's time to serve, deep fry the vadas in oil and serve with chutney or tomato sauce.