Rinse and drain moong dal and soak in water overnight or for at least 2 hours.
Drain out all the water. Add the dal to a blender jar.
Add green chili, ginger, cumin seeds, salt, and half of the water.
Blend to make a fine batter.
Take the batter out into a mixing bowl. Add turmeric, rice flour, and the remaining water, and mix well.
Add onions and cilantro. Mix well and rest the batter for five minutes.
Preheat the pan to low-medium heat. Lightly oil the pan.
Pan temperature matters more than anything else for an evenly spread chilla. Keep it on low heat while pouring and spreading the batter. If the pan's too hot, the batter sticks to the back of the ladle and won't spread thin and even.
Ladle ⅓ cup of batter and spread it into a 6-inch circle. Cook on medium heat for 2 to 3 minutes. Add a few drops of oil and then carefully flip the chilla.
Drizzle oil on top and cook for another 2 to 3 minutes or until the chilla has light brown marks. Take the chilla out and repeat with the remaining batter.
Between chillas, lower the heat so the pan can cool down a bit; on cast iron, a couple of wet paper towels wiped across the surface cools it faster. That brief cooldown is what gives you time to spread the next chilla thin and even.