In a mixing bowl, mix together rava, rice flour, maida, salt together. Add enough water to make a thin batter of running consistency without any lumps.
Add finely chopped green chilies, cumin seeds, black pepper corns, ginger, curry leaves (if using)and mix well. If the batter is not thin enough, add more water. Check and adjust salt.
Heat a tawa pan or girdle and let it become hot. Scoop some water in your palm and splash it on the pan. The water droplets will sizzle and the pan will dry out. Simmer the flame to medium.
Sprinkle chopped onion evenly over the hot pan.
Immediately pour the thin batter in a circular motion on top of the onions with a cup. Do not level the top using ladle but just fill out the gaps by pouring the batter.
Drizzle a few drops of oil evenly around the dosa. Cook over medium low flame till it turns crisp. No need to flip it. Just fold it and transfer to a plate.
Serve this onion rava dosa piping hot with coconut chutney and sambar.