About 20 minutes before making the dough, peel the potatoes & boil them until they are tender. Drain & mash them. Use the potatoes while they are still warm. Stir the yeast into the warm water in a large mixing bowl. Add the flour, potatoes & salt in two additions. Mix together. Knead for 10 minutes. Place the dough in a lightly oiled bowl, cover & let rise till doubled. Divide the dough in half & shape into a ball. Place each ball into a well oiled 23 cm roind baking pan & stretch the dough towards the edges. Cover, let sit for 10 minutes & then stretch a little more. Cover again & leave until it has doubled. Preheat the oven to 200ºC . Dimple the dough with your finger. Sprinkle with olive oil & spread with tomatoes, capers, salt & oregano. Bake for 25 to 30 minutes until golden. Cool on wire racks & eat at room temperature.