Prep the ingredients. Slice chicken into thin strips. Core and slice the bell peppers. Thinly slice the onion. Mince the garlic. Grate the Parmesan. Zest and halve the lemon. This makes the cooking smooth and quick.

Season the chicken. Pat chicken dry and toss with 1–1.5 tablespoons Cajun seasoning, a pinch of salt, and black pepper. Add smoked paprika if your Cajun blend is mild. Coat evenly.

Boil the pasta. Bring a large pot of salted water to a boil. Cook pasta until just shy of al dente (about 1 minute less than package). Reserve 1 cup pasta water, then drain.

Sear the chicken. Heat 1 tablespoon olive oil in a large skillet over medium-high. Add half the chicken in a single layer and cook 2–3 minutes per side until browned and just cooked through. Remove to a plate. Repeat with remaining oil and chicken. Do not overcook.

Cook the vegetables. In the same pan, lower heat to medium. Add butter, then the onion and bell peppers. Season with a pinch of salt and 1 teaspoon Cajun seasoning. Cook 5–6 minutes until tender and lightly caramelized. Add garlic and cook 30 seconds until fragrant.

Build the sauce. Pour in chicken broth and scrape up browned bits. Simmer 1–2 minutes to reduce slightly. Stir in heavy cream and bring to a gentle simmer, not a hard boil.

Cheese and balance. Whisk in Parmesan until melted and smooth. Add lemon zest and a squeeze of lemon juice to brighten. Taste and adjust with salt, pepper, and more Cajun seasoning if needed.

Bring it together. Add the cooked pasta and most of the chicken to the skillet. Toss, adding splashes of reserved pasta water as needed to loosen and gloss the sauce. Simmer 1–2 minutes until the pasta finishes cooking and the sauce clings.

Finish and serve. Top with remaining chicken, chopped parsley or green onions, and a final squeeze of lemon if you like. Serve hot with extra Parmesan at the table.