pasta reshrimp cipe

8 ounces fettuccine, linguine, or spaghetti 1 pound medium shrimp, peeled and deveined Kosher salt and freshly ground black pepper, to taste 8 tablespoons unsalted butter, divided 4 cloves garlic, minced ½ teaspoon dried oregano ½ teaspoon crushed red pepper flakes 2 cups baby arugula or spinach ¼ cup freshly grated Parmesan 2 tablespoons chopped fresh parsley leaves