Boil the pasta: Bring a large pot of salted water to a boil. Cook pasta until just shy of al dente.
Reserve 1 cup of pasta water, then drain.
Season the chicken: Pat the chicken dry. Season with salt, pepper, and half the Italian seasoning.
Sear the chicken: Heat 1 tbsp olive oil in a large skillet over medium-high. Add chicken in a single layer.
Cook 3–4 minutes per side until golden and cooked through. Transfer to a plate.
Sauté aromatics: Lower heat to medium. Add remaining oil and the butter.
Stir in onion with a pinch of salt. Cook 3–4 minutes until soft. Add garlic and red pepper flakes; cook 30–60 seconds until fragrant.
Deglaze: Pour in wine or broth.
Scrape up browned bits. Simmer 1–2 minutes until slightly reduced.
Add tomatoes and seasoning: Stir in crushed tomatoes and remaining Italian seasoning. Simmer 5–7 minutes to thicken slightly.
Taste and season with salt and pepper.
Make it creamy: Lower heat. Stir in the cream and Parmesan until smooth. If too thick, loosen with a splash of pasta water.
Combine: Return chicken and any juices to the skillet.
Add the drained pasta and toss to coat. Add pasta water, a little at a time, until the sauce clings silkily to the noodles.
Finish with basil: Stir in chopped basil off the heat. Squeeze a few drops of lemon if you like a brighter finish.
Serve: Top with extra Parmesan, black pepper, and basil leaves.
Serve hot.