Cook the fettuccine according to package instructions until al dente, then drain.
In a large skillet, heat olive oil over medium heat. Add garlic and sauté until fragrant, about one minute.
Add the shrimp to the skillet and season with Cajun seasoning, salt, and pepper. Cook until shrimp are pink and opaque, about 3–4 minutes.
Stir in the diced bell pepper and cook for 2 minutes until slightly softened.
Pour in the heavy cream and stir to combine, bringing the mixture to a gentle simmer.
Add the cooked fettuccine to the skillet, tossing to coat evenly with the sauce. If the sauce is too thick, add a splash of reserved pasta water.
Sprinkle in the Parmesan cheese and stir until melted and well combined.
Taste and adjust seasoning, if necessary. Afterward, remove from heat and let it sit for a minute.
Serve hot, garnished with chopped parsley for freshness.