Bring a pot of salted water to a boil. Add in your fettuccine pasta and cook according to the package instructions. Drain, and set aside.
Place your butter in a large saucepan, and heat over medium heat until the butter is melted. Add your garlic and cook for 1 minute, or until the garlic is fragrant but not browned. Add your oregano and flour to the saucepan. Cook for another minute to lightly cook the flour.
Gradually pour your milk into the butter/flour mixture, whisking very well after each addition to prevent clumps. Add your salt. Cook the mixture, whisking constantly, over medium heat for about 6 to 8 minutes, or until it starts boiling and thickens enough to coat the back of a spoon.
Remove your mixture from the heat, and add in your grated cheese. Stir together until the cheese is melted and incorporated. Add in your cooked pasta, and toss to coat in the sauce. Top with parsley and more grated cheese if desired!