Preheat the oven to gas 6, 200°C, fan 180°C.
Drizzle the tomatoes with oil, season and roast on a baking tray for 20 minutes, until the skins have split. Remove from the vines.
Warm the croissants on a separate baking tray for 4-5 minutes. Cut the croissants in half horizontally and fill each with Parma ham slices, torn mozzarella, basil leaves (if using) and a few roast tomatoes, crushing the tomatoes slightly. Season with black pepper and eat warm.
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For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home and view the full Food safety at home video.