Preheat the oven to 220°C (425°F/Gas 7).
Toast the bread directly on the oven rack until both sides are just lightly golden. Rub garlic over one side of each slice, then put on a baking tray and drizzle 1 tablespoon of olive oil over each. Cover each with 2 slices of tomato, then a little drizzle of oil and season with salt and a few grinds of pepper. Scatter some of the oregano over, then top with the mozzarella slices and the rest of the oregano. Put in the oven and cook until the mozzarella starts to melt. Put on plates, give a final drizzle of olive oil and scatter over the basil leaves. Give one or two grinds of black pepper and serve at once.