Heat the oil in a pan and fry the onions and garlic until for about 10 minutes until golden brown. Stir in the ginger and green chilli, if using and cook for 1 minute, stirring.
Add the garam masala to the pan with the turmeric, chilli powder and a pinch of salt and cook for another minute, stirring. Add the tomatoes, tomato puree and bring to the boil stirring continuously. Add four tablespoons of water, stir well to combine, then reduce the heat and simmer for 10 minutes until the sauce is well reduced.
Cut the chicken into 2.5cm (1in) cubes and then add to the pan with a few tablespoons of water to the reduced down sauce. Slowly bring to the boil, then reduce the heat and simmer gently for about 10 minutes or until the chicken is cooked through and completely tender. Stir in the cooking cream and simmer gently for another few minutes until well combined. Season to taste.
To serve, arrange the basmati rice and chicken korma on warmed plates and scatter over the coriander. Place the naan breads in a separate dish to pass around at the table along with the mango chutney.