Ground Spices: grind all the spices in a food processor and set aside.
Heat the oil in a nonstick skillet over medium heat. When hot, place the chicken thighs skin side down and cook for 5-6 minutes until golden brown. Flip the chicken and cook for an additional 4 minutes. Once chicken is cooked remove from the pan and let rest on a baking sheet.
Add the onions to the hot pan and cook for 8-10 minutes until golden. Add the ginger, garlic, green chiles and cook for 30 seconds. Add the ground spices, reserving a teaspoon of the spices to garnish. Cook for 10-15 minutes until everything is caramelized.
Add the tomatoes, tomato paste, salt, chili, and turmeric then turn the heat to medium and stir fry. Cook for 20 minutes until you achieve a thick, rich sauce.
Turn off the heat, let the tomato mixture cool, then blitz in a blender until smooth. Add 5-6 tablespoons of water to ensure the sauce isn't too thick. Return to the pan, add the cooked chicken thighs and 1/4 cup of water and increase the heat to medium-high. Cook until you start to see the oil separate from the sauce, about 3-4 minutes.
Garnish with chopped cilantro and a sprinkle of the reserved spice blend. Serve with basmati rice, chapati or fresh salad.