Heat the oven to 200°C/400°C. Put the tomatoes, garlic, chilli and olive oil on a baking sheet, season well and toss. Roast for 25-30 minutes then stir through the basil. Switch the oven to the grill on high.
Place the bread on a baking sheet. Split the tomatoes between the 4 pieces of bread then top with the mozzarella. Drizzle over any leftover oil from cooking the tomatoes. Put the sandwiches underneath the grill and cook until browned. Serve drizzled with balsamic vinegar.
Nutrition information is an estimate and will vary depending on the exact ingredients used.