Place the potatoes and sweet potatoes in a large saucepan and cover with plenty of cold water. Cover and bring to the boil over high heat. Remove from heat and drain in a colander (take care not to break up the potatoes). Set aside for 15 minutes or until cooled to room temperature.
Brush a barbecue plate with 1 tablespoon of the oil to grease and preheat on high. Place the potatoes and sweet potatoes on preheated barbecue, drizzle with the remaining oil and season with salt and pepper. Cook, tossing occasionally, for 12-15 minutes or until golden and tender. Transfer to a serving bowl and serve warm.
