Preheat the oven to 200°C.
Heat oil in an ovenproof pan over low heat, add tomatoes and sugar, then roast for 12 minutes.
Season the sea bass fillet with salt and pepper and score the skin side.
Heat oil and butter in a frying pan and cook the fish skin-side down for two minutes.
Turn the fillet and cook for 30 seconds until done, then keep warm.
Add torn rocket and balsamic vinegar to the fish pan and simmer for five minutes until thickened.
Toss the remaining rocket in a bowl with a drizzle of olive oil.
Plate the rocket salad, top with fish, drizzle with pan juices, and garnish with chives and roasted tomatoes.