Preheat oven to 200ºC (390ºF). Place the potato and 1 tablespoon of the oil on a baking tray and toss to coat. Roast for 25 minutes. Add the fish, asparagus and capers to the tray and drizzle with the remaining oil. Roast for 15–20 minutes or until the fish is cooked through and the potato is golden.
Combine the butter and dill and spoon over the fish to serve. Serves 2.