How to Make It
Heat oven to 450° F. Place the potatoes in a roasting pan or on a baking sheet. Drizzle with 3 tablespoons of the oil and toss to coat. Sprinkle with 1/2 teaspoon of the salt and 1/4 teaspoon of the pepper. Roast for 20 minutes. Stir and roast for 10 minutes more.
Move the potatoes to the sides of the pan. Pat the cod fillets dry with paper towels. Place the fillets in the center of the pan. Drizzle with the remaining oil and sprinkle with the remaining salt and pepper.
Redistribute the potatoes around the fillets. Roast until the fillets are the same color throughout and flake easily, about 10 minutes. Top with the lemon zest and chives (if using).