Bring a large pot of salted water to a rolling boil. Add penne pasta and cook according to package directions until al dente (10-12 minutes), reserving 1/2 cup pasta water before draining.
Pat chicken dry with paper towels, cut into 1-inch pieces, and season all sides with salt and black pepper.
Heat olive oil in a large 12-inch skillet over medium-high heat. Add chicken in a single layer and cook 3-4 minutes per side until golden brown and cooked through (165°F internal temperature), then transfer to a plate.
Reduce heat to medium, add butter to the same skillet, and let it melt while scraping up browned bits. Add minced garlic and sauté 30-45 seconds until fragrant.
Sprinkle flour into the skillet and whisk continuously for 1-2 minutes to create a roux, then slowly pour in chicken broth while whisking to prevent lumps.
Bring mixture to a gentle simmer for 2-3 minutes until slightly thickened, then reduce heat to medium-low and add heavy cream. Stir in Parmesan cheese until completely melted and smooth.
Add chopped sun-dried tomatoes, Italian seasoning, and red pepper flakes (if using) to the sauce. Let simmer gently for 2-3 minutes to allow flavors to meld, then taste and adjust seasoning.
Return cooked chicken to the skillet, add drained pasta, and toss everything together to coat evenly. If sauce is too thick, add reserved pasta water 1 tablespoon at a time until desired consistency is reached.
Remove from heat, garnish with torn fresh basil leaves and extra Parmesan cheese if desired. Serve immediately while hot and creamy.