Preheat the oven to 200°C / Fan 180°C / Gas Mark 5.
Using a knife, thinly slice the sweet potato and beetroot into wafer-thin slices. Spread out onto paper towel to remove any excess moisture.
Place the slices into a large bowl and sprinkle with the oil and seasoning - toss to coat evenly.
Arrange the slices in a single layer on baking trays and roast for 20 minutes, turning them after 10 minutes.
Remove from the oven when crisp and golden and spread out on a paper towel until cool.