Mix the marinade ingredients in a bowl.
Coat the chicken in the marinade and refrigerate for 12 hours or overnight.
Preheat the grill to its highest setting.
Grill chicken for 4 minutes per side, then baste with butter and lemon juice.
Preheat the oven to 200°C.
Roast the chicken for 12 minutes until cooked through.
Fry the grated onion in butter for 5 minutes until soft.
Add the ginger and garlic and cook for one minute.
Stir in tomato purée, chillies, and chilli powder and cook for 3 minutes.
Reduce heat, stir in cream, and simmer for one minute.
Add chicken breasts to the sauce and season with salt and pepper.
Serve chicken on plates drizzled with sauce and sprinkled with fresh coriander.
Serve alongside basmati rice and naan bread.