Start by grilling the cod. Remove the inside from the corn bread and set aside. Bake the onions together with the potatoes at 170ᵒC for 40 minutes. After roasting, peel the onions and cut them into pieces. With your hands or with a kitchen hammer slightly punch the potatoes. Place the onions, the potatoes, the previously cooked turnip greens and the cod in a baking dish or inside the corn bread. Drizzle with olive oil, add chopped garlic and serve.