Preheat the oven to Gas Mark 6, 200°C, fan 180°C.
Scatter the tomatoes, onion, pepper and courgette into a large shallow baking dish. Add the garlic and herbs. Cut 4 thin slices from the lemon and reserve. Cut the remainder into chunks and add to the roasting dish.
Drizzle with olive oil and bake for 30 minutes until all the vegetables are tender.
Cut the fish into 4 pieces, place on top of the veg and top with a lemon slice. Drizzle with a little extra oil.
Season lightly and bake for about 15-20 minutes or until the fish flakes easily.