Wash the tomatoes and halve. Preheat the oven to 200°C/gas mark 6.
Place the pizza bases on a non-stick baking tray and spread with a little passata. Sprinkle over the dried oregano. Arrange the torn ham slices, tomatoes and mozzarella on top and transfer to the oven.
Bake for 10 minutes, until the base is crisp and the cheese is bubbling and golden. Scatter over the basil leaves and chilli flakes to serve.