Cook pasta according to packet instructions. Drain, and set aside.
In a large frying pan, heat oil over medium-high heat. Fry the onions and garlic until onions soften, about 5 minutes. Stir in the tomatoes, chicken, basil, salt and optiional chilli. Reduce heat to medium, cover frying pan and simmer for about 5 minutes, stirring frequently.
Toss sauce with pasta to coat and heat through. Serve with Parmesan.