Preheat oven to 350º F. Heat a large drizzle of the olive oil in a large frying pan. Cook the onion, celery and carrot over medium heat until just tender, then add the garlic and cook for two more minutes. Add the diced tomatoes, tomato paste, oregano and sugar and simmer until slightly thickened, about 10 minutes. Season with salt and pepper.
Arrange the fish in a single layer in a baking dish. Add the parsley and lemon juice to the tomato mixture, then layer over the fish. Sprinkle the panko crumbs over the mixture and drizzle olive oil over the crumbs. Bake for approximately 20 minutes or until the fish is just opaque. Garnish dish with a generous drizzle of lemon juice and parsley.