Marinate chicken in yogurt and Tandoori spices. Brown in frying pan and finish in a preheated 400-degree oven for 15 minutes. Boil water and pour over couscous that has been lightly toasted in a saucepan. Pour in enough water to cover the couscous, as it absorbs the water add the butter and season with salt and pepper. Place couscous on a plate and top with the roasted chicken including the juices from the pan.