1. In a large saucepan, heat the oil over moderate heat. Add the garlic and cook, stirring, for 1 minute. Add the canned tomatoes, fresh tomato, salt, and red-pepper flakes and bring to a simmer. Simmer the sauce until thick, about 30 minutes.
2. Add the cod and 2 tablespoons of the parsley to the sauce. Bring back to a simmer and continue simmering until the fish is just done, 1 to 2 minutes. Break the fish into small pieces with a spoon.
3. Meanwhile, in a large pot of boiling, salted water, cook the penne until just done, about 13 minutes. Drain. Toss with the sauce. Top the pasta with the remaining tablespoon parsley.
Variation: To make this dish without a trip to the fish market, substitute two six-ounce cans of drained tuna for the cod. Stir it into the tomato sauce and warm for about a minute before tossing with the pasta.
Test-Kitchen Tip: To peel the fresh tomato quickly, make double use of the pasta-cooking water. Bring a pot of water to a boil, core the tomato, and drop it into the water for fifteen seconds. Using a slotted spoon, remove the tomato from the water, peel, and chop it. Then you've got boiling water ready for the pasta.
Wine Recommendation: The adage is white wine with fish, but the tomatoes in this sauce call for a red instead. Try a sprightly Lago di Caldero or an easier-to-find Valpolicella.