In a skillet, sauté oil and onion over medium heat until softened.
Add garlic and cook for 1 minute.
Stir in the tomato sauce, basil, salt, oregano, pepper and cooked chicken. Bring to a boil.
Reduce heat; simmer, uncovered, for 20 minutes.
Meanwhile, cook pasta until al dente according to package directions; drain.
To serve, serve sauce over pasta and sprinkle with Parmesan, if desired.