Scrub the beetroot and cut into thin wedges. Place in a shallow ovenproof dish with the onions and drizzle with the oil. Sprinkle with the caraway seeds and season with a little salt and plenty of pepper. Cook in a preheated oven, 200°C (400°F), Gas Mark 6, for about 1 hour until the vegetables are roasted and tender, stirring once or twice during cooking.
Meanwhile, place the flour and lemon thyme in a bowl, add the butter and rub in with the fingertips until the mixture resembles fine breadcrumbs.
Scatter the goats' cheese over the vegetables and sprinkle with the crumble mixture. Return to the oven for 25–30 minutes until the topping is pale golden. Sprinkle with thyme and serve with a watercress or rocket salad, if liked.