Heat the olive oil in a large skillet over medium heat. Add the onion and sauté until soft and translucent, 4 to 6 minutes. Add the garlic and continue cooking for 2 to 3 minutes, stirring constantly to keep the garlic from browning.

Add the tomatoes and, using a wooden spoon, break them into small pieces. Bring the mixture to a slow simmer and cook, stirring occasionally, for 5 minutes. Season to taste with salt and freshly ground black pepper and simmer for an additional 10 to 12 minutes, or until any excess liquid has evaporated and the sauce has thickened to the desired consistency.

Taste and adjust the seasoning as needed, then stir in the parsley.