For this full-flavored weeknight dinner, fish fillets are baked with a quickly assembled tomato sauce flavored with olives, capers, garlic and oregano. Baking the fish in the sauce makes it difficult to overcook, and has the convenient benefit of being served with simply boiled potatoes.
Preheat the oven to 425˚ F. Rub the bottom of a 9-by-13-inch baking dish with 1 tablespoon olive oil. Season the fish on both sides with salt and pepper; place skin-side down in the dish.
Heat 3 tablespoons olive oil in a large skillet over medium heat until shimmering. Add the onion and cook, stirring occasionally, until tender and lightly browned, about 5 minutes. Add the garlic and cook until softened, about 30 seconds. Add 1/2 teaspoon oregano and the bay leaves and stir to combine. Add the tomatoes, olives, capers and a pinch of salt and bring to a simmer. Cook, stirring occasionally, until just slightly thickened, about 3 minutes.
Pour the tomato mixture all over the fish. Bake until the fish is cooked through, 12 to 15 minutes.
Meanwhile, put the potatoes in a medium saucepan and cover with water by 1 inch; season with salt. Bring to a boil, reduce to a steady simmer and cook until very tender, 10 to 12 minutes. Drain and toss with the remaining 2 tablespoons olive oil and 1/2 teaspoon oregano; season with salt and pepper.
Divide the fish among plates. Spoon the tomato mixture over the top and sprinkle with chopped cilantro. Serve with the potatoes.