Peel and quarter carrots and parsnips. Peel both onions and cut them into slices. Clean and peel the beetroot and also cut it into slices. Wash thyme, shake dry. Pluck off the leaves, except for something to garnish.
Put the carrots, parsnips, beetroot, both onions and thyme leaves in an ovenproof casserole dish. Drizzle olive oil over it, season with salt and pepper. In a preheated oven (electric cooker: 200 °C/ circulating air: 175 °C/ gas: see
manufacturer) cook for 30-40 minutes. Mix lemon juice and honey and sprinkle on vegetables about 5 minutes before the end of the cooking time. Remove from the oven and garnish with thyme.