Bring a large pot of well-salted water to a boil, add the pasta, and cook according to package directions until al dente. Reserve about 1/2 cup of the starchy pasta water, then drain the pasta and set it aside.

While the pasta cooks, pat the chicken breasts dry with paper towels and cut them into bite-sized strips or small cubes.

Season the chicken pieces with about 3/4 teaspoon of the fine sea salt, 1/4 teaspoon of the black pepper, and the Italian seasoning, tossing to coat evenly.

In a large deep skillet or sauté pan, heat the olive oil over medium-high heat until shimmering, then add the seasoned chicken in a single layer.

Cook the chicken for 6–8 minutes, stirring occasionally, until it is lightly golden on the outside and cooked through, then transfer the chicken to a plate and set it aside.

Reduce the heat to medium, add the butter to the same skillet, and once melted, stir in the minced garlic, cooking for about 30 seconds until fragrant but not browned.

Add the sliced sun-dried tomatoes and dried basil to the skillet, stirring for 1–2 minutes so they warm through and infuse the butter and garlic.

Pour in the chicken broth and use a wooden spoon to scrape up any browned bits from the bottom of the pan, then let the mixture simmer gently for 2–3 minutes.

Stir in the heavy cream, the remaining 1/4 teaspoon fine sea salt, the remaining 1/4 teaspoon black pepper, and the red pepper flakes if using, then bring the sauce to a gentle simmer.

Reduce the heat to low and gradually sprinkle in the grated Parmesan cheese, stirring constantly until the cheese has melted and the sauce is smooth and slightly thickened.

Add the fresh baby spinach to the skillet and stir for 1–2 minutes until the spinach is just wilted into the creamy sauce.

Return the cooked chicken and any accumulated juices to the skillet, stirring to coat the pieces in the sauce and letting them warm through for 1–2 minutes.

Add the drained pasta to the skillet with the sauce and chicken, tossing everything together until the pasta is well coated; if the sauce seems too thick, loosen it with a splash of the reserved pasta water a little at a time.

Taste the Tuscan Chicken Pasta and adjust the seasoning with a pinch more salt or black pepper if needed, then serve warm.