Crush the cardamom pods using a mortar and pestle. Remove the husks and crush the seeds a little further.
Cook the sweet potatoes in salted boiling water for 5 minutes until softened but not falling apart. Drain well.
Mix together the olive oil, crushed spices and a little salt and pepper. Drizzle over the potatoes and turn them until coated. Arrange the sweet potatoes in a single layer on the upper rack of the halogen oven. (You will need to cook the sweet potatoes in batches.)
Set the temperature to 250°C (482°F) and cook for 3–5 minutes on each side until golden. Keep warm while cooking the remainder. Serve as a snack with a spicy or soured cream and chive dip, or to accompany roast pork or chicken.