Bring a large pot of salted water to a boil. Cook the pasta al dente, according to package directions. Drain.
Hammer (pound) the chickens to slightly thinner and rub chicken with cajun seasoning each sides.
Melt 2 tablespoons butter in a large pan set over medium-high heat, add the chickens and sear until deeply golden on both sides, 5 minutes per side. Sprinkle the Parmesan cheese. Turn the heat off and pour over the lemon juice. Transfer to a plate.
To the same pan, add 2 tablespoons butter, the garlic, and chili flakes. Cook 1 minute, until fragrant, then pour in the stock and cream. Whisk until smooth. Bring the sauce to a gently simmer and cook 5 minutes, until sightly thickened. Stir in 1 ½ cups parmesan, then toss in the pasta. Cook 2 minutes. Remove from the heat and stir in the parsley.
Serve immediately topped with sliced chicken and parsley.