Bring a large pot of salted water to a boil. Add your fettuccine and cook according to the package directions until it reaches al dente texture. Before draining, reserve about half a cup of the starchy pasta water. Drain the rest and set the pasta aside.

Pat the shrimp dry with a paper towel to ensure a good sear. In a medium bowl, toss the shrimp with 1 tablespoon of Cajun seasoning. In a large skillet, melt 2 tablespoons of butter over medium-high heat. Add the shrimp in a single layer and cook for 1-2 minutes per side until pink and opaque. Remove the shrimp from the skillet and set them aside on a plate.

In the same skillet, melt the remaining 2 tablespoons of butter. Add the sliced red bell peppers and cook for 2 minutes until slightly softened. Stir in the minced garlic and cook for 30 seconds until fragrant. Pour in the heavy cream and the remaining Cajun seasoning and smoked paprika. Bring to a gentle simmer, then stir in the Parmesan cheese until the sauce thickens slightly.

Add the cooked pasta and the seared shrimp back into the skillet with the sauce. Toss everything together until the pasta is thoroughly coated. If the sauce is too thick, add a splash of the reserved pasta water to reach your desired consistency. Season with salt and pepper as needed.

Divide the pasta into four warm bowls. Garnish generously with fresh chopped parsley and an extra sprinkle of Parmesan cheese. Serve immediately while the sauce is creamy and hot.