Preheat the oven to 375°F with a rack in the center position. Set a metal cooling rack inside of a large rimmed sheet pan.
In a medium sized bowl combine the yogurt, lemon juice, ginger, garlic, turmeric, chili powder, cayenne, cinnamon, cumin, cilantro, salt and pepper.
Pat the chicken dry with paper towels. Place on a large cutting board, breast side down with the neck facing toward you. Using good-quality kitchen shears, hold the neck and cut along one side of the spine, separating it from the ribs. Be sure to cut as close to the spine as possible. Repeat on the other side of the spine. If you are having difficulty, rotate the bird so the tail faces you and cut from the other side. Flip the chicken breast-side up. Using the palms of your hands, press along the breastbone; you might hear a crack. This should flatten the chicken completely.
Coat chicken all over with the yogurt mixture.
Arrange the chicken on the prepared baking sheet. Alternatively, you can set the chicken into a roasting pan.
Bake the chicken for 15 minutes per pound, about 1 hour 25 minutes or until the internal temperature of the chicken reads 165°F on an instant read thermometer.
Serve the chicken over the lemon rice sprinkled with cilantro with raita alongside, if using.