In 8-inch nonstick skillet over medium heat, heat remaining 1 tablespoon oil. Add the potato mixture (the skillet will be very full) and cook, shaking often, until almost set, about 8 minutes. Gently shake skillet to make sure potato mixture is loose. Place a plate over the skillet and invert onto plate. Carefully slide the omelet, cooked side up, back into the skillet. Cook until set, about 3 minutes longer. Shake skillet to loosen and slide omelet onto clean plate. Serve hot or let cool 45 minutes. Cut into 4 wedges to serve.