Use a pestle and mortar or a food processor to combine walnuts, parsley, garlic, lemon and olive oil into a paste. Season with freshly ground salt and black pepper.
Use a kitchen towel to pat dry the fish. Cover each piece of fish with the walnut mixture, pressing slightly to ensure it sticks.
Place the fish on a lined baking sheet and cook at 220 C for 10 minutes, then grill for 5 minutes.
Thinly slice red and green cabbage as well as onion and place onto a serving tray. Place fish onto cabbage, then combine all the dressing ingredients and drizzle over the fish.
Garnigs with parsley and enjoy with a glass of white wine!