Heat oil in large pan on medium-high heat. Sauté onions until translucent. Add ginger garlic paste, stir for 5 minutes.
Turn heat to medium, add tomatoes, stir until pulpy. Optionally you can add tomato paste for a thicker, sweeter taste. (You can optionally puree this mixture in a blender for a more creamy, smooth sauce.)
Add all spices, stir for 5 minutes.
Add chicken and potatoes, and let them cook for 20 minutes, stirring occasionally.
When the chicken and potatoes are cooked, garnish with cilantro, and simmer on medium-low for 10 minutes. Serve over white rice.