Prep the chicken. Pat the chicken dry and cut into bite-size pieces.
Season with 1 teaspoon kosher salt, 1/2 teaspoon black pepper, and the Italian seasoning. This step builds a flavorful base.
Boil the pasta. Bring a large pot of salted water to a boil. Cook the pasta until just shy of al dente. Reserve 1 cup of pasta water, then drain.
Don’t overcook—the pasta will finish in the sauce.
Sear the chicken. Heat olive oil in a large skillet over medium-high. Add the chicken in an even layer. Cook 4–6 minutes, stirring once or twice, until golden and cooked through.
Transfer to a plate and keep warm.
Start the sauce. Reduce heat to medium. Add butter to the same skillet. Stir in the garlic and cook 30–45 seconds until fragrant—don’t let it brown.
Build the roux. Sprinkle in the flour.
Whisk for 1 minute to form a paste and cook off the raw flour taste.
Whisk in liquids. Gradually whisk in the chicken broth until smooth, then add the cream. Simmer 2–3 minutes until slightly thickened.
Add cheese and seasoning. Off the heat, stir in the Parmesan until melted and silky. Add a pinch of red pepper flakes if using.
Taste and season with salt and pepper. If the sauce is too thick, loosen with a splash of pasta water.
Finish the pasta. Return the chicken to the skillet, then add the drained pasta. Toss over low heat until everything is coated and warmed through.
Add lemon zest and a squeeze of lemon juice to brighten the flavors.
Adjust and serve. If needed, use more pasta water to reach a glossy, flowing sauce that clings to the pasta. Top with extra Parmesan and chopped parsley. Serve hot.