In a large bowl, add the raw shrimp and 3 teaspoons to 1 tablespoon of Cajun seasoning (depending on your heat preference) and toss to coat evenly. Cover and let it marinate in the fridge for 30 minutes to 1 hour.

While the shrimp is marinating, cook the pasta according to the instructions in the package until al dente. Set aside 1 cup of pasta water (optional).

Heat 2 tablespoons of extra-virgin olive oil in a large skillet over medium-high heat and add the marinated shrimp. Cook until they turn pink and form a C shape, about 2-3 minutes per side. Remove the shrimp from the skillet and set aside.

In the same hot skillet, add 2 tablespoons of unsalted butter. Once melted, add the red onions and minced garlic. Sauté for 1-2 minutes until fragrant, being careful not to burn the garlic.

Lower the heat to medium. Pour in 1½ cups of chicken stock and 1½ cups of heavy cream, stirring to combine. Scrape the brown bits from the bottom of the skillet with a wooden spoon for added flavor.

Add the fresh lemon juice and lemon zest, then stir. Taste the sauce and adjust seasoning with more Cajun seasoning.

Stir in the grated Parmesan cheese and red pepper flakes (if using). Add the cooked pasta to the sauce and toss to coat. If the sauce is too thick, add some of the reserved pasta water. Then, add the cooked shrimp and combine everything.

Garnish your Cajun shrimp pasta with fresh minced parsley and lemon slices. Serve immediately on its own or with crusty bread on the side.