Preheat the oven to gas 6, 200°C, fan 180°C. Place the carrots and parsnips in a large roasting tin in a single layer, drizzle with olive oil and season. Roast in the oven, turning occasionally, for 30 minutes. Remove from oven.
Mix the maple syrup, mustard and orange juice and zest in a jug and pour over the semi-roasted vegetables. Return the veg to the oven and roast for a further 10-15 minutes or until caramelised and sticky.