While you are preparing the shrimp and alfredo portion of the recipe, cook the fettuccine according to package instructions.
In a medium bowl, combine the raw shrimp, 1 tsp olive oil, 2 tsp of Cajun seasoning, 1 tsp of salt, and 1/2 tsp pepper. Stir to coat the shrimp in the seasoning.
In a large skillet, heat 1/2 Tbsp of olive oil over medium-high heat. Cook the shrimp in 2 batches to not overcrowd them in the skillet. Cook 2 minutes per side until pink and cooked through. Remove to a plate when cooked. Then add another 1/2 Tbsp of olive oil and cook the second batch. Remove the second batch of cooked shrimp to a plate and set aside.
Add 1 Tbsp of olive oil to the skillet over medium-high heat. Add the broccoli and onion, season with salt and pepper. Cook until the broccoli starts to slightly soften (It will finish cooking in the alfredo), about 2-3 minutes.
Add garlic and cook until fragrant, about 30 seconds. Add the chicken broth, heavy cream, and 2 tsp of Cajun seasoning. Let simmer until the liquid starts to reduce slightly, about 5 minutes.
Add the parmesan cheese and cook until all of the cheese has melted and the sauce has thickened a little (it will thicken more after you add the pasta and shrimp).
When the fettuccine is done cooking, pull it from its water and place into the skillet with the alfredo. Toss the pasta in the sauce until it’s well coated. Add more parmesan cheese to thicken, if needed. Taste for seasoning, adding more salt or pepper if necessary.
Add the shrimp and toss it with the pasta and sauce. Divide between bowls and top with a little more grated parmesan cheese.