Preheat the oven to 200°C/fan oven 180°C/gas mark 6.
You could also use regular potatoes – but they may need a bit longer in the oven – or try pumpkin or butternut squash.
Slice each sweet potato lengthways into 6 wedges and put them in a roasting tin. Add the vegetable oil, season with black pepper and toss to coat. Roast in the oven for 35 to 40 minutes, or until tender, turning them over after 20 minutes.
Spice up the sweet potatoes by sprinkling them with 1 tsp of cumin seeds.