In a large saucepan or frying pan, add the extra virgin olive oil and heat up on a medium low heat.
Once warm, add the thinly sliced onions, the peeled but whole cloves of garlic, and a pinch of salt.
Mix the ingredients well and cook slowly, so as to soften the onion without browning it, stirring occasionally.
Once the onions are transparent and soft [approx 5-7 minutes], add the red pepper flakes and mix, allowing these to cook for about a minute.
Next, add the canned chopped tomatoes to the onion mixture and mix well.
To the sauce, add a cup of water, mix well again, and bring the sauce to a light simmer. Put a lid on the saucepan, reduce the heat to low, and allow to simmer for 12-15 minutes, stirring occasionally.
In the meantime, in a large pot of salted boiling water, cook the rigatoni pasta as per the package directions, ensuring it remains al dente.
Once the sauce is ready, remove the garlic cloves.
As soon as the rigatoni are ready, drain them [quickly, you don't need to remove all the cooking water], and add them to the saucepan together with the parsley.
Mix the pasta to the sauce while keeping the pan on a low flame.
Serve the pasta while hot and enjoy!