In a large skillet cook the onion, green pepper and pimiento in 2 tablespoons of the oil over moderate heat, stirring occasionally, until vegetables are softened. Transfer vegetables to a bowl. In the skillet heat the remaining oil over moderately high heat until hot and add the potatoes. Saute, stirring occasionally, for 15 to 20 minutes, or until tender and crisp. Stir in the vegetable mixture and correct seasoning. Heat over moderately low heat until hot and serve.