Finely chop the onions or pulse them a few times in a food processor. Place the onions in a muslin cloth (or cheesecloth) and squeeze to remove as much water as possible. Set aside.
Whisk one of the eggs in a small bowl and set aside. Heat oil in a small frying pan, and add the whisked egg. Cook the egg in the form of scrambled egg and set aside.
Place the turkey mince in a bowl. Add the onions, the green chilies, chopped coriander leaves, the scrambled egg and the spice mixture. Mix thoroughly. The best way to mix the chapli kabab mixture is to use your hands and knead the ingredients together for 2 – 4 minutes.
Keep the mixture in the fridge for about an hour to marinate and chill.
Remove the chapli kabab mixture from the fridge, and then add the chopped tomatoes, raw egg, and chickpea flour. Start off with adding ½ cup chickpea flour (besan), and then add more if needed. Mix thoroughly.
Heat oil in a large frying pan. Once the oil is hot, do a taste test by frying off a small patty. If needed, adjust salt and spices. In case the mixture is breaking, add some more chickpea flour to bind the kababs together.
Once you are satisfied with the seasonings in the mixture, portion out some of the mince mixture to form a small patty. Chapli kababs are on the thinner side so flatten the mixture accordingly.
Press a tomato slice on top of the patty, and then fry the chapli kababs tomato side down. Let the chapli kabab fry for about 2 – 3 minutes, then flip over and fry on the other side till crispy and golden brown. Once you flip the patty, the tomato will have caramelized and turned a beautiful reddish-brown colour.