Boil the penne in salted water until al dente.
Finely chop the tomatoes, onion, and garlic.
Heat olive oil in a pan and sauté the garlic and onion.
Add the tomatoes and simmer until the sauce thickens.
Add the cooked penne to the sauce and toss together.
Season with salt and pepper, sprinkle with Parmesan cheese, and serve.