Cook fettuccine according to package instructions, set aside. Reserve ½ cup pasta water.
Mix cajun seasoning ingredients in a small dish.
Lay shrimp out on a plate, pat with paper towels until dry. Drizzle with 2 tbsp olive oil. Season with 1 tbsp cajun seasoning, set aside remaining seasoning for the alfredo sauce.
Heat 1 tbsp olive oil in large skillet over medium/high heat. Add shrimp and cook on each side for 2 minutes until crisp. Remove shrimp from skillet. Set aside on a clean plate.
Add chicken broth to the same skillet and stir to deglaze. Lower heat to medium/low, add in heavy whipping cream, and remaining cajun seasoning. Bring to a simmer then add parsley, lemon juice, and Parmesan and stir until melted, season with salt and pepper, to taste.
Add cooked fettuccine pasta to the skillet with cajun alfredo sauce. Cook for 1-2 minutes on med/low while tossing pasta in the sauce until sauce is thickened. If sauce is too thick in texture, add ¼ cup pasta water to make it silky again.
Top with cajun shrimp. Garnish with parsley, Parmesan, and serve with lemon wedges.