To make the vegetables, light the barbecue about 30 minutes before you want to eat, so that the flames die down, the coals have a coating of grey ash and produce a steady heat. Lightly oil the tomatoes, peppers and aubergine and arrange the on the hot barbecue (or place under a hot, preheated grill). Cook until charred all over and starting to collapse, turning occasionally.
Put the vegetables into a large bowl, cover with cling film and set aside to sweat for 10 minutes. Remove and discard the core and seeds from the peppers, then remove and discard the tomato and aubergine skins. Roughly chop all the vegetables and return them to the bowl. Add the garlic and red onion, then toss with the oil and vinegar. Stir through the herbs and season well with salt and pepper.
To make the seabass, mix together the reserved herb stalks, tarragon and lemon thyme. Scrunch them up in your hands to release the oil, and then finely chop. Stuff the fish with the herbs and place on two layers of kitchen foil. Wrap the fish up in the foil and place on the barbecue for 10 minutes.
Carefully open up the foil and spoon in the vegetables. Serve with crusty bread.