Preheat the oven to 350 degrees. Split the loaf of bread in half, lengthwise; set the bread, crusts side down, on a baking sheet. In a mixing bowl combine the cheese, onion, olive oil, vinegar, oregano and olives; season to taste. Spread the mixture over each bread half. Bake until hot.
Remove from oven. Spread the hot loaves with tomato slices, then drape thin slices of ham over tomates and eat hot, accompanied with salad.