Preheat oven (electric cooker: 200 °C/circulating air: 180 °C/gas: see manufacturer). Peel, wash and cut sweet potatoes into cubes of approx. 4 cm. In an ovenproof dish, mix with oil, ½ tsp. salt and spice.
Place in a hot oven (e.g. with the fish) and bake for about 20 minutes until the edges are golden brown.