Heat the oven to 230 C, 210 Fan , Gas Mark 8. Slice the tomatoes in half across their circumference and place snugly in a roasting tin. Drizzle with the olive oil and grind over plenty of black pepper.
Roast for 25 minutes until tender. Meanwhile beat together all the dressing ingredients.
Serve the tomatoes on warm plates, spooning over any liquid from the roasting tin. Pour over the dressing and serve with crusty bread to mop up the delicious juices.