Bring a large pot of salted water to a boil and cook the pasta until just shy of al dente (about 1–2 minutes less than package directions). Reserve 1 cup pasta cooking water, drain pasta, and set aside.

Season the chicken with salt, pepper, garlic powder, and Italian seasoning.

In a large skillet over medium-high heat, warm olive oil. Sear the chicken for 3–4 minutes per side until golden and just cooked through (internal temperature ~165°F / 74°C). Remove chicken to a plate and tent with foil.

Reduce heat to medium. Add butter to the skillet. Sauté shallot/onion until translucent (about 2 minutes), then add minced garlic and red pepper flakes; cook 30–60 seconds until fragrant.

Pour in chicken broth and scrape up browned bits from the bottom of the pan. Let the liquid reduce by about a third (2–3 minutes).

Stir in the diced tomatoes and sun-dried tomatoes (if using). Simmer for 2 minutes.

Lower heat and add the heavy cream, stirring to combine. Allow sauce to warm gently and thicken slightly (2–3 minutes).

Stir in grated Parmesan until melted and the sauce is smooth. If sauce is too thick, whisk in reserved pasta water a little at a time to reach desired consistency. Taste and adjust seasoning; add lemon juice if using.

Slice or cube the cooked chicken and return to the skillet to warm through and finish cooking in the sauce for 1–2 minutes.

Add drained pasta to the skillet and toss to coat evenly. Stir in chopped basil/parsley. If needed, add more pasta water to loosen the sauce so it clings to the pasta.

Serve immediately topped with extra Parmesan and fresh herbs.