Place besan, salt, baking powder, turmeric, coriander, chilli powder, ajwain seeds and water in a medium bowl. Whisk with a balloon whisk until smooth. Set aside for 5-10 minutes.
Heat a medium saucepan/crepe pan on medium-low. Drizzle a small amount of olive oil (approximately 1/2 teaspoon) on the pan. Using a ladle, gently drop half a cup of batter on the pan. Using the back of the ladle, swirl the batter fanning out from the centre so it spreads in a circular shape about 18-20cm in diameter. Increase heat to medium and let the batter cook for a few seconds. When bubbles start to appear on the surface, scatter onion, tomato, green chilli and coriander leaves on the surface. Gently flip the omelette to cook the side with the veggies on for approximately 1-2 minutes.
Remove on to a serving plate and serve immediately with green chutney or your favourite hot sauce. Repeat with the remaining batter and veggies.
Notes
Although chickpea flour (besan) is of a uniform consistency everywhere, sometimes it maybe more coarse than fine. This affects the amount of water to be used and the thickness of the batter. Ideally, the batter should be like a pancake batter. Just thin enough to pour without being runny. If you feel the batter is too thin, add a tablespoon of the besan to even it out and vice versa (with the water if it is too thick).