Start by preparing the rice stuffing; place the rice and hot water in a saucepan along with a little water. Bring to the boil over a high heat, then cover with a tight-fitting lid and simmer over a gentle heat for 10-12 minutes until the rice has absorbed the rice. Remove from the heat and keep covered to one side.
Preheat the oven to 200°C.
Remove the rice from the saucepan and use a fork to mash it a little to break up its texture. Add the diced green pepper and seasoning, stirring well to mix. Use the rice to stuff the cavity of the sea bass.
Arrange the mango slices down the sides of a ceramic roasting dish, leaving a large space in the middle where the fish will sit. Carefully lay the stuffed fish into that space. Top with overlapping, alternate slices of green pepper and and tomato all the way down the centre of the fish. Drizzle with olive oil.
Roast in the oven for 25-30 minutes until the fish is just cooked. Remove from the oven and allow to sit for a few minutes. Sprinkle the chopped oregano down the centre of the fish, on top of the slices of green pepper and tomato before serving.
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