In a pan/kadai or in a pressure cooker, Add sliced onion, turmeric powder, coriander powder, red chilli powder, black pepper powder, garam masala powder, chicken masala powder, ginger garlic paste, curry leaves and coconut oil. Using your hands, very thoroughly mix everything together until well combined.
Now add the cleaned chicken and mix and combine everything together untill well combined.
Switch on the stove; cover and cook for 15-20 minutes or until chicken turns tender. Stir in between to avoid burning; allow it to cook on a medium-low flame.If your cooking in pressure cooker; cook it for 1 whistle and switch off the heat and allow the pressure to settle down.(Note : During cooking, the water from the chicken oozes out forming a gravy in which it gets cooked, and so you do not need to add extra water or if you prefer more gravy then add 1/4 cup of hot water)
Open the lid and add quartered tomatoes and green chilles and cook it on high heat for another 5 minutes. Adjust the gravy consistency according to your preferences.Taste test it and adjust the salt and if there is lot water in it, cook it on high heat for another couple minutes so that all water evaporates or till you get the desired gravy consistency.
Remove from the fire; sprinkle little coconut oil on top and keep covered until it's ready to serve.(Note : It enhances the flavor)
Tasty easy one pot nadan chicken curry is ready to serve. Serve as a side dish for for Rice or with Chapathi/Rotior with any Indian Bread. Enjoy !.