Cut chicken thighs or breasts into bite-sized pieces about 1 inch. Pat dry with paper towels. Season all sides generously with Italian seasoning, salt, and black pepper. Let sit while you prepare other ingredients.

Heat olive oil in large 12-inch skillet over medium-high heat. Add seasoned chicken pieces in single layer with space between each. Cook without moving for 3-4 minutes until golden brown on bottom. Flip and cook another 3 minutes until browned. Remove chicken to plate and set aside. Chicken doesn't need to be fully cooked yet.

In same skillet over medium heat, add diced onion. Cook 3-4 minutes until soft and translucent, stirring occasionally. Add minced garlic and cook 30 seconds until fragrant. Don't let garlic burn or it will taste bitter.

Pour crushed tomatoes into skillet with onions and garlic. Add chicken broth and stir to combine. Season with Italian seasoning, salt, and black pepper. Stir well and bring to simmer. Let sauce bubble gently for 2-3 minutes to develop flavors.

Add uncooked pasta directly into the tomato sauce. Stir to coat pasta with sauce. If pasta isn't fully submerged, add more chicken broth or water. Bring to simmer, then reduce heat to medium-low. Cover skillet and cook 12-15 minutes, stirring every few minutes to prevent sticking.

When pasta is almost tender, add seared chicken back to skillet along with any juices from the plate. Stir everything together gently. Cover and cook another 5 minutes until chicken is cooked through and pasta is tender. Check pasta for doneness.

Remove from heat. Stir in grated Parmesan cheese until melted. If making creamy version, add heavy cream now and stir until combined. Add fresh chopped basil and toss everything together. Taste and adjust seasoning with more salt or pepper if needed.

Let stand 2-3 minutes to thicken slightly. Sauce should coat pasta nicely. Serve hot with extra Parmesan cheese and fresh basil on top. Add red pepper flakes if desired.