Mix the yeast in with the warm water. Add in the mashed potatoes. Add the salt to the flour. Slowly stir in the flour mixture to the wet ingredients. Gentle knead together until the dough forms a ball. Do not over knead. Place in a large bowl and cover with a cloth. It should double in size in 30 minutes. Turn it onto a flat floured baking pan and press it into an oval shape about 8 inches long. Decorate however you please. Sprinkle a little salt and pour the oil over the top.