Preheat oven to 220°C/390°F (200°C fan-forced).
In a large mixing bowl, toss the potatoes with the oil, salt and pepper. Spread on a baking tray with a rim at least 2cm/0.8" high. Roast for 20 minutes.
Meanwhile, mix all the sauce ingredients together. Add to the tray, toss with the potatoes, return to the oven for 10 minutes.
Pat the fish dry with paper towels. Sprinkle each side with the salt and pepper.
Place fish on top of puttanesca sauce. Drizzle all over with the 1 ½ tablespoons of oil. Bake 15 minutes or until fish is just cooked through.
Remove from the oven. Drizzle with a bit more olive oil, scatter with basil and reserved fennel fronds. Serve with warm, crusty bread!
