Bring a large pot of salted water to a boil over medium-high heat. Add the fettuccine and cook until al dente, 8-10 minutes, or according to the package directions.
To a large skillet over medium heat, add the smoked sausage pieces. Cook for 2-3 minutes per side, or until they are golden brown. Remove the sausage from the skillet, and tent with foil to keep warm.
Using the same skillet, melt the butter over medium heat. Add the minced garlic and cook for about 1 minute.
Pour in the heavy cream. Then, add the Cajun seasoning, salt, pepper, and crushed red pepper flakes. Stir to combine. Bring to a boil, stirring occasionally.
Reduce the heat to low. Simmer the sauce for 6-8 minutes, or until it begins to thicken.
Add parmesan cheese, stirring until it’s melted.
Add the cooked fettuccine and sausage to the skillet, tossing to coat them evenly in the sauce.
Garnish with chopped parsley. Serve.