In a mixing bowl, add 1 cup of besan (gram flour), 1/4 teaspoon of turmeric powder, 1/2 teaspoon of red chilli powder, and salt to taste.
Finely chop 2 medium-sized tomatoes, 1 green chilli, and a handful of fresh coriander leaves. Add these to the mixing bowl.
Gradually add water to the bowl, mixing continuously to form a smooth batter. The consistency should be slightly thinner than a dosa batter.
Heat a non-stick tawa or pan on medium flame and lightly grease it with oil.
Pour a ladleful of the batter onto the tawa and spread it evenly to form a thin circle.
Drizzle a few drops of oil around the edges of the chilla and cook until the bottom side is golden brown, about 2-3 minutes.
Flip the chilla and cook the other side for another 2 minutes or until it is fully cooked and has a nice golden color.
Transfer the chilla to a plate and repeat the process with the remaining batter.
Serve the Tomato Besan Chilla hot with green chutney or ketchup.