Cook the pasta in salted water until al dente, about 8-10 minutes, then drain and cool.

Prepare the vegetables by dicing tomatoes and onions, and slicing basil into ribbons.

In a bowl, combine cooled pasta, olive oil, and balsamic vinegar; toss to coat.

Fold in garlic, tomatoes, optional onions, and basil.

Top with parmesan cheese and mix gently.

Serve immediately or refrigerate for later, refreshing with olive oil or vinegar if needed.