Pat chicken pieces dry with paper towels. In a medium bowl, toss chicken with 1 tablespoon olive oil, 1/2 tsp salt, 1/4 tsp black pepper, and 1/2 tsp Italian seasoning until evenly coated.

Heat a large skillet over medium-high heat. Add the seasoned chicken in a single layer, ensuring not to overcrowd the pan (cook in batches if necessary). Cook for 4-6 minutes, flipping occasionally, until golden brown and cooked through. Remove chicken from the skillet and set aside.

While chicken cooks, bring 8 cups of salted water to a rolling boil in a large pot. Add the pasta and cook according to package directions until al dente. Reserve 1 cup of pasta water, then drain the pasta and set aside.

In the same skillet used for chicken (do not clean it, the fond adds flavor), melt 2 tablespoons of unsalted butter over medium heat. Add the minced garlic and sauté for 1 minute until fragrant.

If using flour, sprinkle 1/4 cup all-purpose flour into the melted butter and garlic. Whisk constantly for 1-2 minutes to create a roux.

Gradually whisk in 2 cups of chicken broth, scraping up any browned bits from the bottom of the pan. Bring to a simmer, then slowly stir in 1.5 cups of heavy cream. Add 1 tsp Italian seasoning, 1/4 tsp red pepper flakes (if using), 1/2 tsp salt, and 1/4 tsp black pepper. Simmer gently for 5-7 minutes, stirring occasionally, until the sauce begins to thicken slightly.

Reduce heat to low. Gradually stir in 1.5 cups of grated Parmesan cheese until melted and smooth. Taste and adjust seasoning as needed. If the sauce is too thick, add a splash of the reserved pasta water.

Add the cooked chicken, drained pasta, and optional fresh spinach to the skillet with the sauce. Toss everything gently until the pasta and chicken are evenly coated and the spinach has wilted.

Divide the Creamy Parmesan Chicken Pasta among bowls. Garnish with fresh chopped parsley and extra grated Parmesan cheese, if desired. Serve hot.