Put the flour in a large bowl, then stir in the yeast and a large pinch of salt. Make a well in the centre, pour in 175ml warm water and the oil and bring together with a wooden spoon to make a soft, fairly wet dough. Turn out onto a lightly floured surface and knead for 5-8 mins until smooth. Divide the dough into four balls and arrange on a floured tray, well spaced apart. Cover with a tea towel and set aside for about 40 mins-1 hr until doubled in size.
Heat the oven to 240C/220C fan/gas 8 and put a baking tray in the oven to heat up. Roll the dough balls out on a floured surface into long baguette sticks about 22-25cm long, place on the hot tray and bake for 10-12 mins until puffed up and golden, then leave to cool. Can be made a few hours ahead of baking.
To assemble, split the bread down one side and neatly layer in the tomato, ham, mozzarella and rocket, if using. Mix the pesto with the olive oil, drizzle over, halve and serve.