In a 14 to 16-inch saute pan, heat 4 tablespoons olive oil until almost smoking. Add the onions and garlic and saute 3 to 5 minutes, until soft and light golden brown. Add the tomatoes and the chili flakes and flatten tomatoes with a fork, allowing them to release their juices. Cook for 10 minutes, until tomatoes have completely fallen apart. Add the wine and bring to a boil. Add the cod, mussels, and cockles, reduce heat to a simmer and cover, allowing to cook for 10 minutes, until fish is cooked through. Remove from heat, sprinkle with parsley, drizzle with remaining olive oil, season with salt and pepper and serve.