Preheat oven to 400F. In a large saucepan set over moderate heat, heat oil until hot, and add the onion and cook it, stirring occasionally for 4 minutes. Add the garlic and cook for 3 to 4 minutes more, or until the onion and garlic are golden in color. Now add the tomatoes, oregano, red pepper flakes and salt and pepper to taste and simmer the tomatoes for 6 to 8 minutes, or until lightly thickened. Add the basil and shrimp and cook, stirring gently, for 1 to 2 minutes, or until the shrimp are just turning pink. Place cooked pasta in a large bowl, gently stir in shrimp and tomato mixture, 2 tablespoons of the parsley and half of the feta cheese. Transfer to an oiled 3 quart shallow flameproof baking dish and sprinkle with the remaining feta cheese and parsley. Cover loosely with foil, place in the oven and bake for 20 minutes, or until bubbling. Run under the broiler until golden.