Using a pair of sharp kitchen shears, cut on either side of the backbone of the chicken, removing it.
Turn the chicken over and flatten with the palm of your hand.
Combine all the marinade ingredients together and rub the yogurt mixture over the chicken and under the skin, making sure it's completely coated.
Allow to marinade for at least 45 minutes up to 24 hours covered in the fridge.
Preheat the oven to 250°C/480°F (or as hot as your oven goes) on the broiler/oven grill setting. Line a baking tray with foil and place a wire rack on top.
Place the chicken on a wire rack over a roasting dish or baking sheet. Place the chicken in the oven then turn the heat down to 180°C/350°F and allow to roast for 45-60 minutes drizzling with oil half way through as the yogurt marinade will form a crust and dry out a little. If you want a deeper color on the skin, allow the chicken to broil under the broiler/grill of the oven for a few minutes at the end of cooking.
Once cooked, remove the chicken from the oven and allow to rest for 10 minutes. The chicken is cooked when the juices run clear or when the meat reaches 73ºC/165°F on a meat thermometer. I would recommend removing the chicken from the oven when it reaches 160°F/70°C as it will continue cooking as it rests. Carve the chicken once rested and serve.
Serve the Tandoori chicken with naan bread, rice and cucumber salad.