Bring a large pot of salted water to a boil. Cook penne according to package directions until al dente. Reserve ¼ cup pasta water, then drain.
Heat olive oil in a large skillet over medium heat. Add chicken, season lightly with salt and pepper, and cook for 4–5 minutes until golden and cooked through. Remove chicken from the skillet and set aside.
In the same skillet, melt butter over medium-low heat. Add garlic and cook for 30 seconds, just until fragrant.
Stir in chicken broth and simmer for 1–2 minutes.
Reduce heat to low and add heavy cream, Parmesan cheese, Italian seasoning, parsley, and red pepper flakes if using. Stir until smooth and creamy.
Return cooked chicken to the skillet, then add the drained penne. Toss to coat evenly. Use reserved pasta water as needed to loosen the sauce.
Simmer gently for 2–3 minutes, then remove from heat. Taste and adjust seasoning.
Garnish with fresh herbs and serve warm.