Cook the fettuccine in salted boiling water according to package directions. Reserve ½ cup pasta water, then drain.
Toss the shrimp with 1 tbsp Cajun seasoning. Heat the olive oil in a large skillet over medium-high heat and sear the shrimp 2 minutes per side. Remove and set aside.
In the same skillet, melt the butter. Sauté the bell peppers 3 minutes, then add the garlic and cook 1 minute more.
Stir in the heavy cream, chicken broth, and remaining 1 tbsp Cajun seasoning. Simmer 3 minutes, then whisk in the Parmesan until melted and smooth.
Return the shrimp to the skillet, add the fettuccine, and toss to coat, loosening with reserved pasta water as needed. Top with parsley and serve hot!