Crumble the yeast in a bowl. Mix water with oil, pour over the yeast and stir until it has dissolved. Add salt and flour. Knead the ingredients extensively to form a smooth dough. Dust some flour over the dough. Cover the dough and let rise for 45 minutes. Sprinkle a baking sheet with flour. Knead the dough again on a floured surface and cut into quarters. Shape each piece into a round loaf and place on the tray. Cover the loaves and let them rise for 30 minutes. Preheat the oven to 225 C. Cut the loaves lengthways several times with a sharp knife. Bake on the lower rail in the oven for about 30 minutes. Let cool on a wire rack.
The preparation of the topping (tomatoes etc.) has already been described here several times!