In a large pot of salted boiling water, cook the fettuccine according to package instructions until al dente. Drain and set aside.
In a large skillet, heat olive oil over medium heat. Add the sliced smoked sausage and sauté for about 5-7 minutes, or until they are browned and heated through. Remove them from the skillet and set aside.
In the same skillet, add the diced onion and cook for 3-4 minutes until translucent. Add the minced garlic and cook for an additional 1 minute, stirring occasionally to avoid burning.
Pour the heavy cream into the skillet with the onions and garlic, stirring to combine. Allow the cream to heat through for 2-3 minutes. Gradually mix in the Parmesan cheese, Cajun seasoning, and paprika until the cheese melts and the sauce thickens. If the sauce is too thick, you can thin it out with a splash of pasta water.
Add the cooked fettuccine and smoked sausage back to the skillet, tossing to coat everything evenly in the Alfredo sauce. Season with salt and pepper to taste.
Remove from heat and let sit for a minute. Plate the pasta and sauce mixture into bowls or on plates, garnished with chopped green onions or parsley for a pop of color.