Preheat your oven to 250°C.
Blend all the sauce ingredients except the cornflour together in a blender until well mixed.
Put the sauce in a pan and bring to the boil.
In a small dish, stir the cornflour and a little water together until smooth.
Add to the boiling sauce and stir well.
Simmer for 5 minutes and then strain.
Finely chop the ginger, red onion and chilli and scatter over the fish with the tomatoes and the strained sauce.
Bake for 20 minutes.
Scatter the whole fish with the picked fresh coriander leaves and serve with plain rice.
