Bring a large pot of salted water to a boil over high heat. Add the pasta and cook until al dente according to the package directions. Reserve 1 cup of the water and drain the pasta. Set aside.

In a medium bowl, toss the shrimp with 1/2 the olive oil, 1 tablespoon of the lemon juice and 1/2 of the cajun seasoning until coated.

Heat the remaining olive oil and butter in a large skillet medium-high heat. Add the shrimp to the skillet in a single layer being sure not to crowd the pan and cook until no longer transluscent, approximately 2 minutes per side. Transfer the shrimp to a plate. (You may need to work in batches.)

Add the onion to the skillet and cook until softened, approximately 3-4 minutes. Stir in the garlic and cook until fragrant, stirring constantly, about 1 minute. Stir in the seafood stock and simmer about 3-4 minutes until it’s reduced by half.

Add the tomatoes, tomato paste, heavy cream, parmesan, remaining cajun seasoning, remaining ½ teaspoon salt, and remaining lemon juice and zest. Simmer over low heat, stirring occasionally, until the sauce is thick enough to coat the back of a wooden spoon, approximately 5 minutes.

Add the pasta to the skillet and toss until coated. Cook until the pasta is tender and coated in the sauce. If the sauce seems too thick, stir in the reserved pasta water 1 tablespoon at a time until the desired consistencly. Stir in the shrimp and season to taste with salt and pepper.

Serve the pasta with the shrimp and sprinkle with parmesan, parsley and red pepper flakes, if desired.