Cook the pasta. Bring a large pot of salted water to a boil. Cook pasta until just shy of al dente. Reserve 1 cup of pasta water, then drain.

Season the shrimp. Pat shrimp dry. Toss with 1 tablespoon Cajun seasoning, a pinch of salt, and a drizzle of olive oil. Set aside.

Sear the shrimp. Heat a large skillet over medium-high. Add 1 tablespoon butter and 1 tablespoon olive oil. Cook shrimp in a single layer for 1–2 minutes per side until just opaque. Transfer to a plate. Do not overcook.

Sauté the aromatics. Reduce heat to medium. Add remaining 1 tablespoon butter. Stir in onion and bell pepper with a pinch of salt. Cook 4–5 minutes until softened. Add garlic and remaining Cajun seasoning. Cook 30 seconds until fragrant.

Deglaze. Pour in stock. Scrape up any browned bits from the pan. Let it simmer 1–2 minutes to reduce slightly.

Make it creamy. Lower the heat and stir in heavy cream. Simmer gently for 2–3 minutes until it starts to thicken. Add cherry tomatoes if using and cook 1 minute.

Add cheese and balance. Stir in Parmesan until melted. Season with salt and black pepper. Add lemon zest and a small squeeze of lemon juice to brighten.

Toss with pasta. Add drained pasta to the skillet. Toss to coat, adding splashes of reserved pasta water as needed to create a silky sauce that clings.

Finish with shrimp. Return shrimp and any juices to the pan. Toss for 30–60 seconds to warm through. Adjust seasoning with salt, pepper, or more Cajun seasoning to taste.

Serve. Top with chopped parsley or green onions, extra Parmesan, and a pinch of red pepper flakes if you like heat.