In a large pot of boiling salted water, cook the pasta according to package directions.
Place the shrimp in a medium bowl and toss with the Cajun seasoning.
In a large skillet over medium-high heat, heat the butter and the olive oil. Add the shrimp to the pan and cook for about 1-2 minutes per side or until it turns pink. Remove the shrimp from the skillet and reserve.
Into the same skillet, add the heavy cream, garlic powder and ground black pepper. Stir and simmer on low heat for about 4-5 minutes. Add the Parmesan cheese and mix well until slightly thick. If the creamy sauce gets too thick, you can add additional heavy cream or some of the pasta water.
Drain the cooked pasta, reserving about 1/2 cup of the pasta water.
Add the cooked pasta and shrimp to the skillet. Mix gently with the sauce until well combined. If the dish looks a bit dry (and needs a bit more creaminess), you can add some of the reserved pasta water.
Season to taste with additional Cajun seasoning and garnish with sliced green onions and parsley (optional). Serve immediately!