In a skillet heat the oil over moderate heat until it is hot, add the onion and salt and pepper to taste, and cook the onion, stirring occasionally, for 5 to 7 minutes, or until it is golden. Add the tomato, garlic, basil, and thyme and cook the mixture until thick, stirring occasionally, about 3 to 5 minutes more. Spoon half the tomato mixture into an oiled shallow flameproof baking dish just large enough to hold the fish in one layer, arrange the fish fillets on top of the tomato mixture, and sprinkle them with salt and pepper, to taste. Spoon the remaining tomato mixture over the fish and bake it in a preheated 375 degree F oven, covered with foil, until the fish just flakes about 15 minutes.
With a spatula, carefully transfer the fish to a large plate. Bring the tomato mixture in the baking dish to a simmer over moderate heat, add the broth and cornstarch mixture and the tomato paste, and simmer the sauce, stirring, until it is thickened. Let it cool. Carefully transfer the fish and its sauce to a flat freezer container with a tight-fitting lid, arranging the fish in a single layer. Freeze the fish for up to one month.
To reheat: Defrost the fish, covered, in the refrigerator. Transfer the fish to a baking dish and bake the fish, covered with foil, in a preheated 375 degree F oven for 15 to 20 minutes, or until it is heated through. Correct the seasoning, adding salt and pepper, to taste, and sprinkle the baked halibut with the minced parsley before serving.
Recipe courtesy Gourmet Magazine