Stir together the oil, vinegar, oregano, salt and some pepper in a small bowl. On a work surface, spread out the bread and brush the oil and vinegar mixture onto all of the slices.
Layer half of the bread slices with the red peppers, salami, prosciutto, mortadella, cucumber slices, basil and pepperoncini. Top with the remaining bread slices. Using a serrated knife, cut away the crusts from each sandwich. Cut each sandwich into thirds. Place them on a tray and serve.