Preheat oven to 400 degrees F. Place potatoes in a large roasting pan or on a large rimmed baking sheet; drizzle with oil and turn to coat evenly. Add bell pepper and onion. Season with 1/4 teaspoon salt and pepper.

Roast the vegetables, turning the potatoes once or twice and moving the pepper and onion pieces around so they brown evenly, until the potatoes are starting to brown and are almost tender, about 35 minutes.

While the vegetables are roasting, finely chop parsley, lemon zest, oregano and garlic together to make gremolata. Season halibut with remaining 1/4 teaspoon salt and pepper, then sprinkle with 2 teaspoons gremolata.

Remove the pan from the oven. Increase oven temperature to 450 degrees. Push the vegetables to the sides of the pan and place the halibut in the center. Spoon some of the onions and peppers over the halibut. Arrange the potatoes around the edges, turning the browned sides up.

Roast until the vegetables are browned and tender and the halibut is opaque in the center, 10 to 15 minutes more, depending on the thickness of the fish. Sprinkle the remaining gremolata on top. Arrange the halibut and vegetables on a platter or individual plates. Serve with lemon wedges.

How to Skin a Fish Fillet

You can ask to have the skin removed from a piece of salmon or halibut fillet at the fish counter, but it is also easy to do it yourself. Place the fillet, skin-side down, on a cutting board. Use a thin sharp knife to cut between skin and flesh at the tip. Grasp the skin with your free hand and ease the knife carefully between skin and flesh, keeping the knife pointed slightly toward the skin, until skin is removed.