Rinse the moong dal thoroughly under running water 2 to 3 times until the water runs clear. Soak in enough water for 4 to 5 hours or overnight. Drain completely.
Add the soaked dal, ginger, green chilies, and 2 to 3 tablespoons of water to a blender or mixer grinder. Grind to a smooth, thick batter. The consistency should be like pancake batter, thick but pourable.
Transfer the batter to a bowl. Add chopped coriander leaves, cumin seeds, hing, turmeric powder, and salt. Mix well. If the batter feels too thick, add 1 to 2 tablespoons of water and stir.
Heat a non-stick tawa or flat pan on medium heat. Drizzle a few drops of oil and spread it with a cloth or paper towel.
Pour a ladleful of batter onto the center of the tawa. Spread it gently in a circular motion to form a round pancake about 6 inches in diameter. Do not spread it too thin.
Drizzle half a teaspoon of oil around the edges and a few drops on top. Cook for 2 to 3 minutes until the bottom turns golden brown and the edges start lifting.
Flip carefully using a flat spatula. Cook the other side for 1 to 2 minutes until golden spots appear. Press gently with the spatula for even cooking.
Remove the chilla from the pan and keep it warm. Repeat with the remaining batter, greasing the pan lightly before each chilla.
Serve hot with green chutney, tomato ketchup, or yogurt.
Notes
Use a non-stick or well-seasoned cast iron tawa for best results. If the chilla sticks, your pan may not be hot enough or needs more oil.The batter can be made in advance and refrigerated for up to 2 days in an airtight container. Stir well before using.For a quicker version, use a wet grinder or high-speed blender to reduce grinding time. You can freeze cooked chillas by layering them between parchment paper.Reheat on a hot tawa or in a microwave. Adjust the spice level by adding or reducing green chilies.For extra crispiness, cook on slightly higher heat for the last 30 seconds on each side. If the batter thickens in the fridge, add a tablespoon of water and mix before cooking.