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

Sauté the chicken: While the pasta is cooking, heat the olive oil in a large skillet over medium-high heat. Season the chicken with Italian seasoning, 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.

Build the sauce: Add the garlic and onion to the skillet and cook until softened and fragrant, about 2-3 minutes. Deglaze the pan with the white wine (if using), scraping up any browned bits from the bottom of the skillet. Let the wine reduce slightly, about 1-2 minutes.

Create the creamy base: Pour in the chicken broth and bring to a simmer. Reduce the heat to medium-low and stir in the heavy cream. Let the sauce simmer for a few minutes to thicken slightly.

Incorporate the spinach and cheese: Add the spinach to the skillet and cook until wilted, about 1-2 minutes. Stir in the Parmesan cheese until melted and smooth.

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

Finish and serve: Stir in the butter, sun-dried tomatoes, and lemon juice. Season with salt, pepper, and red pepper flakes (if using) to taste. Garnish with fresh basil and additional Parmesan cheese before serving.