Preheat the oven to 190C/375F/Gas 5.
Heat the olive oil in a frying pan over a medium heat. Add the onion, garlic and chorizo.
Fry for 4-5 minutes until the oil runs out of the chorizo and the onions soften.
Add the thyme, olives and tomatoes and stir to combine.
Season well with salt and freshly ground black pepper, before transferring the mixture to an ovenproof dish.
Using a sharp knife, slash skin of the sea bass diagonally along each side so that the flesh is exposed and place sprigs of thyme into the slashes.
Season the sea bass with salt and freshly ground black pepper and place on top of the chorizo mixture.
Drizzle over the olive oil and cook in the oven for 20-25 minutes, until the fish is tender and cooked all the way through.
To serve,take the cooking dish to the table.