In small resealable food-storage plastic bag, place remaining 1/4 cup white chocolate chunks and the oil; partially seal bag. Microwave on High 30 seconds. Squeeze bag until chunks are smooth. If necessary, microwave 15 to 30 seconds longer. Cut small hole in 1 corner of bag. Squeeze bag gently to drizzle white chocolate over bars. Refrigerate until chocolate is set, about 20 minutes. For bars, cut into 6 rows by 6 rows. Serve at room temperature.