Cook the pasta: Bring a large pot of salted water to a boil. Add the pasta and cook according to package directions until al dente. Reserve about 1 cup of pasta water before draining.

Sear the chicken: While the pasta is cooking, heat the olive oil in a large skillet over medium-high heat. Season the chicken with salt and pepper. Add the chicken to the skillet and cook until browned and cooked through, about 5-7 minutes. Remove the chicken from the skillet and set aside.

Sauté aromatics: Add the chopped onion to the skillet and cook until softened, about 3-5 minutes. Add the minced garlic and cook for another minute until fragrant.

Deglaze and simmer: If using, pour in the white wine and scrape up any browned bits from the bottom of the skillet. Let the wine reduce slightly, about 2 minutes. Add the chicken broth and bring to a simmer.

Create the sauce: Stir in the heavy cream and Parmesan cheese. Reduce the heat to low and simmer for 5-7 minutes, or until the sauce has thickened slightly.

Combine and finish: Add the cooked pasta and chicken back to the skillet. Toss to coat everything in the sauce. If the sauce is too thick, add a little of the reserved pasta water until it reaches your desired consistency.

Brighten and serve: Stir in the chopped parsley and lemon juice. Season with salt, pepper, and red pepper flakes (if using) to taste. Serve immediately, garnished with extra Parmesan cheese.