Sautéing the vegetables
Position a rack in the center of the oven and preheat to 450°F. Heat a heavy, large, ovenproof skillet over high heat. Add 1/4 cup oil and heat 10 to 15 seconds. Add the onion, bell pepper and chile. Toss to blend. Add the diced tomatoes and garlic. Sauté until tender but not yet brown, about 8 minutes.
Completing the sauce
Add the oregano and thyme sprigs and about 1/2 teaspoon salt. Add the wine to the skillet. Simmer, stirring occasionally, until the wine has almost evaporated, 3 to 4 minutes. Stir in the tomato sauce. Reduce the heat to medium. Stir in the olives and capers and simmer 1 minute to blend.
Cooking the fish
Arrange the fish fillets in the sauce and spoon a little sauce over each. Drizzle the fillets with a little more olive oil. Bake in the preheated oven until the fish is cooked through, about 10 minutes.
Serving the fish
Transfer the fish to serving plates. Spoon some sauce around each. Garnish with fresh oregano or thyme leaves.
For the Tomato Sauce:Sautéing the aromatics
Heat a large sauté pan over medium-low heat. Add the oil and, when it begins to flow freely in the pan, add the onions, garlic, and oregano and sauté, stirring occasionally, until tender but not yet browned, 5 to 7 minutes.
Coring and seeding the tomatoes
While the aromatics cook, prepare the tomatoes. With a small, sharp knife, carefully cut out the stem end of each tomato. Cut the tomatoes in halves and squeeze out the seeds into a bowl. Coarsely chop the tomatoes and set aside.
Cooking the tomatoes
Stir the tomatoes and sugar into the pan with the aromatics. Hold a fine-meshed sieve over the pan and pour the seeds into the strainer, letting their juices fall into the pan; discard the seeds. Reduce the heat to very low, cover and cook, stirring occasionally, until the tomatoes have broken down and the sauce has thickened, 2 to 3 hours.
Pureeing the sauce
When the tomato mixture has cooked down, insert the coarse disc into a food mill and position the mill on top of a large mixing bowl. Taste the tomatoes and, if necessary, stir in a little sugar to enhance their sweetness. Ladle the tomato mixture in batches into the food mill and turn the handle to puree. Discard the skins and fibers left inside the food mill.
Storing the sauce
To store any sauce you aren't using right away, ladle it into small storage containers. Let the sauce cool then refrigerate or freeze. Makes 6-8 cups.