In a small bowl, whisk the yogurt until it is completely smooth and creamy. Set aside.
Pat the chicken pieces dry and season them with salt and turmeric powder.
Heat 2 tablespoons of oil in a large pan or Dutch oven over medium-high heat. Add the chicken pieces in a single layer and sear for 3-4 minutes per side, until lightly browned. Remove the chicken to a plate. It will not be cooked through yet.
In the same pan, add the remaining 2 tablespoons of oil. Once warm, add the cumin seeds and cinnamon stick and cook for 30 seconds until fragrant. Add the sliced onions and sauté for 8-10 minutes, until soft and golden brown.
Stir in the green chilies and ginger-garlic paste. Cook for 1 minute until the raw smell is gone. Add the ground cumin, red chili powder, and garam masala. Stir constantly for 30 seconds to toast the spices.
Return the seared chicken and any accumulated juices to the pan. Toss to coat the chicken in the spice mixture.
Remove the pan from the heat completely. Slowly pour in the whisked yogurt, stirring continuously to combine it with the masala. This prevents the yogurt from splitting.
Return the pan to low heat. Cover and let it simmer for 20-25 minutes, or until the chicken is tender and cooked through. Check that the internal temperature reaches 165°F (74°C) with a meat thermometer.
Crush the kasuri methi between your palms and stir it into the curry along with the chopped cilantro. Adjust salt to taste and serve warm.