Preheat oven to 220°C/425°F. Add the sliced sweet potatoes to a large bowl. Drizzle with 1 tbsp of olive oil and season generously with salt and pepper. Sprinkle over the cornstarch, chili powder and cinnamon and stir until evenly coated.
Spread the potatoes on a parchment-lined baking sheet. Transfer to the oven and roast for 20-25 mintues, or until crisp and fork tender. Serve immediately, perhaps with a side of chipotle mayo.