Lift the bread pan out of the machine and fit the blade. Put the dough ingredients in the pan, following the order specified in the manual. Fit the pan into the machine and close the lid. Set to the dough programme.
Meanwhile, fry the mushrooms in 2 tablespoons oil until golden. Leave to cool.
At the end of the programme turn the dough out on to a floured surface and roll it out to a 33 cm (13 inch) square. Arrange the mozzarella slices, basil leaves and mushrooms over the dough. Lightly crush the peppercorns and scatter over the filling with a little salt.
Loosely roll up the dough and transfer to a large, greased baking sheet with the join underneath. Pinch the ends together to seal. Cover loosely with oiled clingfilm and leave in a warm place for 30 minutes.
Flour a large skewer or meat fork and pierce the dough all over, making sure you go right through to the baking sheet. Drizzle with the remaining oil and scatter with sea salt. Bake in a preheated oven, 220°C (425°F), Gas Mark 7, for about 25 minutes until risen and golden. Serve warm or cold.