Mix together the tomatoes and shallot. Add the oil and stir gently to combine. Add enough lemon juice, salt and pepper to taste. At the last minute before serving, add the basil leaves.
Heat the oil in a frying pan over a high heat. Season the sea bass with salt and pepper. When the pan is hot, fry the fish, skin-side down, for 3–4 minutes until the skin is golden brown and crispy. Turn the fish over and cook for a further minute. Remove from the pan and serve with the sauce vierge and rocket leaves.