Bring a large pot of salted water to a boil and cook your fettuccine until it's just al dente, following the package directions. Once it's done, turn off the heat but don't drain it right away. Let the pasta sit in its warm water while you work on the sauce so it stays moist instead of drying out and clumping.
Toss the shrimp with the onion powder, garlic powder, Italian seasoning, paprika, lemon pepper, and half of the Cajun seasoning. Heat olive oil in a large skillet over medium-high heat, then add the shrimp in a single layer. Cook for about two minutes per side until they turn pink and opaque, then pull them out and tent with foil to keep warm.
In that same skillet, melt the butter over medium heat and scrape up any flavorful browned bits left behind. Add the minced garlic and let it cook for about thirty seconds until fragrant, being careful not to let it burn since burnt garlic turns bitter fast.
Pour in the white wine or chicken broth and stir well, scraping the bottom of the pan to release all that seared shrimp flavor into the liquid. Let it bubble for a minute or two until it reduces slightly, then pour in the heavy cream and bring everything to a gentle simmer.
Stir in the freshly grated Parmesan and the remaining Cajun seasoning, then lower the heat and let the sauce simmer for five to six minutes until it thickens up nicely. Taste it and adjust with salt and pepper as needed before moving on.
Drain your pasta, then add it straight into the skillet along with the cooked shrimp. Toss everything gently until the pasta is completely coated in that creamy sauce. Garnish with fresh parsley and serve it up while it's warm and glossy.