In a large bowl, mix the onions, tomatoes, garlic and basil, taking care not to mash or break up the tomatoes too much. Add the balsamic vinegar and extra virgin olive oil. Add salt and pepper to taste. Mix again. Cover and chill for at least an hour. This will allow the flavours to soak and blend together. If you prefer the mixture at room temperature, remove from the fridge half an hour before serving.

Heat grill to High. Place the fish on a baking tray lined with lightly oiled foil. Season, and grill for 4-5 mins until cooked through. Divide the fillets  between serving plates, place the fish, squeeze the lemon juice over the fillets and serve with scattered with the chopped herbsand bruschetta mixture.