Bring a medium pot of salted water to a boil. Add the pasta and cook until just al dente according to package directions. Before draining, reserve 60 ml of the starchy pasta water, then drain and set the pasta aside.

While the pasta cooks, pat the chicken dry and slice into thin strips or small bite-size pieces. Season all over with 0.5 tsp salt, black pepper, Italian seasoning, and chili flakes if using.

Heat the olive oil in a large skillet over medium-high heat. Add the seasoned chicken in a single layer and cook for 4 to 5 minutes, stirring once or twice, until the pieces are golden and just cooked through. Transfer the chicken to a plate and set aside.

Reduce the heat to medium and add the butter to the same skillet. When melted, add the minced garlic and sliced sun-dried tomatoes. Cook, stirring constantly, for 30 to 60 seconds until fragrant but not browned.

Pour in the white wine and stir, scraping up any browned bits from the bottom of the skillet. Let it simmer for 1 to 2 minutes until reduced by about half.

Add the chicken stock and bring to a gentle simmer. Pour in the heavy cream, stir, and let the sauce bubble softly for 3 to 4 minutes until it slightly thickens and coats the back of a spoon.

Lower the heat to low and stir in the grated Parmesan until melted and smooth. Taste and season with the remaining 0.5 tsp salt, adjusting as needed.

Return the cooked chicken and any accumulated juices to the skillet. Simmer for 1 to 2 minutes to warm through and meld the flavors.

Add the drained pasta to the skillet and toss to coat in the creamy sauce. Add the spinach and cook for 1 to 2 minutes, stirring, until the leaves are just wilted. If the sauce feels too thick, add a splash of the reserved pasta water to loosen it to your desired consistency.

Stir in the lemon juice and taste once more for seasoning, adding extra salt or pepper if needed. Divide the Tuscan chicken pasta between two warm bowls, garnish with extra Parmesan and chopped basil or parsley if using, and serve immediately.