Combine chana and masoor dal in a medium bowl. Add enough water and soak dals in water for at least 30 minutes and up to 2 hours. Drain the water from the lentils and transfer them to a blender or food processor. Add ginger, green chilies, salt, and 1~2 tablespoons of water. Grind into a coarse paste.*
Heat about 1~2 teaspoons of oil in each cavity of the appam pan. Add about 1 tablespoon of batter in each cavity, cover and cook, stirring halfway through, until golden brown and crispy all over. Remove onto a plate and set aside. Repeat with the remaining lentil mixture.
To make the Curry:
Heat oil in a sauté pan; add panch phoron and hing. Once the seeds start to splutter, add the onions, ginger, and green chilies. Cook till the onions turn translucent. Add the potato, cover and cook until tender, about 4-5 minutes.
Next add the tomatoes, ground cumin, coriander and red chili powder. Cover and cook till tomatoes turn mushy. Add salt, water and bring the mixture to a simmer. Add the fritters, cook for another minute and serve right away.
Notes
While blending the lentils, make sure not to add too much water. Batter should not too watery or too thick.
Deep fry the lentil mixture instead of using the appam pan.
You can make the lentil fritters with just red lentils - these are called musur daler bora or masoor dal er bora. They can also be made entirely with split peas.
To make the curry ahead of time - keep the gravy or jhol and fried daler bora separate. Mix them just before serving. This will avoid the fritters from absorbing all of the sauce.