Sit the chicken in a large roasting tray, then scrub, halve and add the sweet potatoes.
Spoon over the harissa, 1 tablespoon each of red wine vinegar and olive oil, and a pinch of sea salt and black pepper, then rub until everything is well coated.
Put half the mint into the cavity of the chicken, then roast for 1 hour 20 minutes, or until everything is golden and cooked through.