Tear half the basil leaves into small pieces. Lift the bread pan out of the machine and fit the blade. Add the water, 3 tablespoons olive oil, salt, oregano, flour, sugar and yeast to the pan, following the order specified in the manual.
Fit the pan into the machine and close the lid. Set to the dough programme, adding the torn basil leaves and capers when the machine beeps.
At the end of the programme turn the dough out on to a floured surface and divide it into 8 equal pieces. Roll each piece roughly into a round shape, about 15 cm (6 inches) across, and space them, about 5 cm (2 inches) apart, on 2 large, greased baking sheets. Cover with oiled clingfilm and leave to rise in a warm place for 30 minutes.
Dot with the tomato paste to about 1 cm (½ inch) of the edges. Pile the tomato halves on top. Bake in a preheated oven, 230°C (450°F), Gas Mark 8, for about 15 minutes until risen and the tomatoes are soft.
Meanwhile, chop the remaining basil and mix with the yogurt, mayonnaise, pepper and a little salt. Transfer the buns to serving plates and drizzle with the remaining oil and a little more salt. Serve with the yogurt on the side.