Preheat a fan oven to 180°C. Line a large baking tray with tin foil (to save on the washing up). Chop the potatoes into small cubes about 2cm in diameter. There's no need to be too precise ...
For The Tray Bake: Preheat the oven to 180°C (350°F/Gas Mark 4). On a large baking tray place the sweet potato chunks, red onion wedges and peppers. Drizzle over the olive oil and season with salt.