Place the oil in a heavy bottomed skillet so that the peppers are in a thick (about 2-inch;5cm) layer in the pan. Place over medium heat, and when the peppers begin to sizzle, reduce the heat to low. Stir, cover, and cook until the peppers are very tender and almost creamy, 1 hour, stirring every 10 minutes, and making sure they don't brown. Remove from the heat and season with salt if desired. Eat this warm or at room temperature. It will keep well in the refrigerator in an air-tight container for up to two weeks.