Bring a large pot of salted water to a boil. Cook linguine pasta according to package instructions until al dente. Drain and set aside.
In a medium bowl, toss the shrimp with Cajun seasoning until evenly coated.
Heat olive oil and 1 tablespoon butter in a large skillet over medium-high heat. Add the shrimp and cook for 2-3 minutes per side until pink and opaque. Remove shrimp from skillet and set aside.
In the same skillet, reduce heat to medium. Add remaining 1 tablespoon butter. Add minced garlic and chopped onion, sautéing for 2-3 minutes until fragrant and translucent.
Pour in the chicken broth, scraping the bottom of the skillet to release any browned bits. Let it simmer for 2 minutes to reduce slightly.
Stir in heavy cream, Parmesan cheese, lemon juice, and crushed red pepper flakes. Cook for 3-4 minutes, stirring frequently, until the sauce thickens.
Season the sauce with salt and freshly ground black pepper to taste.
Return the cooked shrimp to the skillet and toss to coat them evenly in the creamy Cajun sauce. Cook for an additional 1-2 minutes to heat through.
Add the cooked linguine pasta to the skillet and toss everything together until the pasta is well coated with the sauce.
Remove from heat and sprinkle chopped fresh parsley over the top before serving.