Start by boiling water in a large pot. Once it reaches a rolling boil, add the fettuccine pasta and a pinch of salt. Cook according to the package instructions until al dente. Once done, drain the pasta, reserving 1/2 cup of the pasta water for later use. Set the pasta aside.
In a mixing bowl, place the peeled and deveined shrimp. Sprinkle the Cajun seasoning evenly over the shrimp and toss them well until they are completely coated.
Heat 2 tablespoons of olive oil in a large skillet over medium-high heat. Once the oil is hot, carefully add the seasoned shrimp. Cook for about 2-3 minutes on each side, or until the shrimp turn a vibrant pink and are opaque. Once cooked, remove the shrimp from the skillet and set them aside on a plate.
With the skillet still on medium heat, add the remaining tablespoon of olive oil. Then, add the minced garlic and sauté for approximately 1 minute, stirring frequently, until the garlic is fragrant but not burnt.
Slowly pour in the heavy cream, stirring as you bring it to a gentle simmer. Once simmering, progressively mix in the grated Parmesan cheese until it melts smoothly into the sauce. If the sauce appears too thick, gradually incorporate the reserved pasta water until you reach your desired creamy consistency.
Add the cooked shrimp back into the skillet, allowing them to mingle with the creamy sauce. Gently fold in the cooked fettuccine, ensuring everything is well combined and coated with the sauce.
Taste the dish and adjust seasoning with salt and pepper as desired. Just before serving, stir in the chopped parsley for a touch of freshness.
Plate the Cajun shrimp Alfredo pasta immediately. For an extra burst of flavor, garnish each serving with fresh lemon wedges to squeeze over the dish before enjoying.