Cut the fish into portions and pat dry with kitchen towel. Place into greased tins.
Steam the fish until cooked, about 15-20 minutes (if you don't have a steamer cover the fish with a little water and cover the dish with foil, put in the oven for 20 minutes, drain the liquid before serving).
Heat the tomato base sauce, just before serving stir in the chopped basil.
You can either pour the sauce over the fish or serve separately.