Preheat the oven to 190C.
Cut the cabbage into 2cm thick slices. Trim the beets and cut them into ½ cm slices. Cut the onion into wedges. Cut the chilli into slices.
Arrange the cabbage, onion and beetroot in a baking dish and scatter the garlic and chilli around them (unpeeled).
Mix the oil with the vinegar then add the marjoram. Brush the vegetables with this, then pour any remaining over them. Season with salt & pepper. Cover the dish with foil, then bake for 15 minutes.
Drizzle or brush them with maple syrup and scatter some walnuts around them.
Bake for another 10-15 minutes, uncovered, until tender and slightly caramelised.
Take the dish out of the oven. Squeeze the garlic flesh out of the skin and rub it into the cabbage. Serve warm.