Bring a large pot of salted water to a boil. Cook the pasta according to package directions until al dente (usually 8–12 minutes). Reserve 1/2 cup pasta water, then drain and set aside.

While the pasta cooks, season chicken strips with salt, pepper, and 1/2 tsp Italian seasoning.

Heat 1 tbsp olive oil in a large skillet over medium-high heat. Sear the chicken until golden and cooked through, about 5–7 minutes total. Transfer chicken to a plate and tent with foil.

Reduce heat to medium. Add remaining 1 tbsp olive oil and 2 tbsp butter to the skillet. Add chopped onion and sauté 3–4 minutes until translucent.

Add garlic and mushrooms (if using) and cook 2–3 minutes until fragrant and mushrooms release juices. Add sun-dried tomatoes and red pepper flakes; cook 1 minute.

Pour in the chicken broth, scraping up any brown bits from the pan. Let simmer for 2–3 minutes.

Stir in heavy cream and cream cheese (if using). Bring to a gentle simmer and cook for 5–7 minutes until the sauce thickens slightly — it should coat the back of a spoon. Tip: simmer gently; rapid boils can break a cream sauce.

Stir in grated Parmesan, lemon zest and juice, remaining Italian seasoning, and adjust salt and pepper. If the sauce is too thick, add reserved pasta water 1–2 tbsp at a time until desired consistency.

Return chicken to the skillet and toss in the cooked pasta. Mix until everything is evenly coated and heated through, about 1–2 minutes.

Serve immediately with extra Parmesan and fresh basil or parsley on top.