Step 1

Preheat oven to 425 degrees. Toss together potatoes, tomatoes, garlic, oregano, 1 tablespoon oil, and 1/2 teaspoon salt. Season with pepper. Arrange potatoes in a 9-by-13-inch baking dish, overlapping them; top with tomatoes.

Step 2

Roast until tomatoes are juicy and potatoes are tender, about 25 minutes. Remove from oven.

Step 3

Rub fish with remaining 1 teaspoon oil, dividing evenly. Season inside and outside of fish with remaining 1/2 teaspoon salt; stuff with lemon slices. Arrange on top of potatoes, shifting tomatoes alongside. Roast until fish are cooked through, about 20 minutes; serve immediately.