In a medium to large pot, cook pasta noodles according to package directions with salt. Once the noodles are cooked to tenderness, pour off and reserve ½ cup pasta liquid and set aside. Drain remaining liquid and keep the noodles warm on the stove top or covered.
In a small bowl combine olive oil, and 2 ½ tablespoons of the cajun seasoning - reserve 1 teaspoon of the cajun seasoning for later use. Coat the deveined and peeled shrimp with this oil and seasoning mixture
Heat a large skillet and melt 2 tablespoons of butter. Add the shrimp in a single layer across the bottom of the skillet. Cook for 2 minutes. Only turn the shrimp over once. Shrimp is cooked when it turns opaque and firm, and depending on the kind of shrimp you use can turn pink. Do not overcook shrimp or it will turn rubbery and chewy. Remove shrimp from the pan and place on a plate so that it will not continue to cook from the heat of the pan.
In the hot pan over medium/ high heat add remaining butter and cook the onion, minced garlic and the reserved 1 teaspoon of cajun seasoning. Saute till onions are translucent, about 4-5 minutes.
Add the heavy cream, and stir. Reduce heat to medium low and allow the cream to come to a low bubble.
Turn off the heat. Add the cheese and stir till smooth and creamy.
Add the cooked pasta and stir to coat.
If the sauce is too thick add some of the reserved pasta water one spoon at a time to thin down to desired thickness.
Sprinkle with fresh chopped parsley before serving.