Bring a large pot of salted water to boil. Cook fettuccine according to package directions until al dente. Reserve 1/2 cup pasta water before draining.

In a small bowl, combine all Cajun seasoning ingredients. Pat shrimp dry and season with half of the Cajun seasoning blend, tossing to coat evenly.

Heat 2 tablespoons olive oil in a large skillet over medium-high heat. Add seasoned shrimp in a single layer and cook for 2-3 minutes per side until pink and cooked through. Remove shrimp to a plate.

In the same skillet, add remaining olive oil. Sauté bell pepper for 3-4 minutes until slightly softened. Add minced garlic and remaining Cajun seasoning, cook for 1 minute until fragrant.

Pour in white wine and let it simmer for 2 minutes to cook off alcohol. Add heavy cream and bring to a gentle simmer, stirring constantly.

Reduce heat to low and stir in parmesan cheese and butter until melted and smooth. If sauce is too thick, add reserved pasta water 1-2 tablespoons at a time.

Add the cooked pasta to the skillet and toss to coat with sauce. Return shrimp to the pan and gently fold in green onions and parsley.

Taste and adjust seasoning with salt, pepper, or additional Cajun seasoning as needed. Serve immediately with extra parmesan cheese if desired.