Preheat oven to 200°C. Place onion and mixed root vegetables into a shallow roasting dish. Toss through olive oil. Roast for 20-25 minutes or until vegetables are just tender. While the vegetables are roasting, wrap the garlic bulb in foil and place on the oven rack and allow to cook until soft – this will take about 15-20 minutes. Reduce the oven temperature to 180°C.