Bring a pot of plain water to a boil. Using a skimmer, carefully lower the tomato into the boiling water. Remove the tomato after about 30 seconds and place it into a bowl of cold water to cool.
Salt the water and cook the pasta according to the package instructions. Reserve some cooking water before draining the pasta.
Meanwhile, peel the tomato and chop it.
Heat the olive oil in a large pan over medium heat. Add the onion, and cook for 3 minutes, stirring, until the onion is translucent. Next, add the garlic and cook, stirring, for another 2 minutes.
Stir in the chopped tomato and tomato paste. Pour in the pasta water to loosen the sauce, and bring to a boil. Reduce the heat, and season with salt, pepper, and oregano. Simmer uncovered for 15 minutes, stirring occasionally.
Add the cooked pasta and stir until combined. To finish, stir in the parsley and serve immediately.
