Preheat the oven to 180°C/350°F/gas mark 5. Peel and portion the sweet potatoes into chips and coat with the cumin, salt, pepper and oil in a bowl.
Lay the chips flat onto a baking tray. Place the tray into the oven and bake for 30-40 minutes, shaking the tray at 10 minute intermittently.
Remove the chips from the oven once they are fully brown and serve warm.