Preheat the oven to 200C/400F/Gas 6.
For the tomatoes, heat the oil over a low heat in an ovenproof frying pan. Add the tomatoes and the sugar and place into the oven for 10-12 minutes. Remove from the oven and set aside.
Meanwhile, for the sea bass, season the fillet with salt and freshly ground black pepper, and score the skin-side with a knife.
Heat the oil and the butter in a large frying pan over a medium heat. Add the sea bass fillet, skin-side down and cook for two minutes.
Turn the fillet over and cook for a further 30 seconds, or until cooked through, then remove from the pan and set aside in a warm place.
Tear the rocket leaves and add to the same pan with the balsamic vinegar. Cook for five minutes to reduce the balsamic vinegar to a thick sauce.
For the salad, place the rocket in a bowl and drizzle with olive oil.
To serve, place the rocket salad onto a large plate and top with the sea bass. Drizzle the sea bass with the balsamic and rocket pan juices and sprinkle with chives. Place the roasted tomatoes around the plate.