Heat 2 tablespoon oil, saute onions till light golden.
Add tomatoes & chili and saute for 2-3 minutes till tomatoes are soft.
Pour the onion, tomato & chili mixture into a blender and blend with water to a smooth paste. Set aside.
Add 2 tablespoon oil into the same pan, and turn to medium heat.
Add garlic & ginger paste, along with whole cumin seeds and saute for a minute till the cumin seeds pop.
Add the blended tomato-chili paste, and cook for 2-3 minutes.
Add salt, black pepper, coriander powder, cumin powder, red chili powder and turmeric.
Turn heat to low, and cook for a minute then add sliced chicken.
Cook on high heat till chicken changes color from pink to white
Turn heat to low, and add a cup of water.
Cook the chicken till meat is tender and oil surfaces. Set it aside.