Preheat the oven to 435ºF (225ºC) . Cut the cabbage into pieces. Peel and thinly slice the onion. Add cabbage and onion in a lined roasting pan. Mix with oil and salt. Bake in center of oven for 20-25 minutes. Add the walnuts when about 10 minutes remaining. Peel the oranges and cut into segments retaining the juice. Let the vegetables cool. Drizzle with the juice and add the orange slices and cranberries before serving.