Pour the oil into a large skillet and place over high heat. Add the onion and bell pepper and saute, stirring, 2 to 3 minutes. Add the potatoes, cumin, salt and red pepper flakes, lower the heat to medium-high and cook, stirring occasionally, for 25 to 30 minutes, or until the potatoes are fork tender and some are browned. The potatoes will begin to stick as they cook. Just continue to turn with a spatula. Stir in half of the green onions, top with the remainder, and serve immediately.