Melt the coconut oil in a pan over a high heat. Add the finely sliced chicken and cook for about 2 minutes. Add the onion, pepper, garlic and grated ginger and cook quickly for another moment or two, still on a high heat. Add the curry spices to the pan and fry for 1 minute to coat the chicken and vegetables with the paste.
Pour the chopped tomatoes, coconut milk and chicken stock into the pan. Cover with a lid and simmer for 5 minutes over a medium to low heat, until the chicken is cooked through. Stir in the coriander and serve with plain rice.