Put a pan of water on to boil for the pasta. Chop the tomatoes roughly and the onion and garlic finely. Put some olive oil into a frying pan (if you're not a low fat freak, don't be too skimpy with the oil). As soon as the water boils switch on the heat under the frying pan, then throw the pasta into the water with some salt and a splash of olive oil and give it a stir. When the pot comes back to the boil you can turn the heat down to medium. Don't let the oil in the frying pan get too hot before throwing in the onion. Fry it fairly gently - the object is to get it soft without letting it brown. Add the tomatoes, garlic and a pinch of salt when you think the onion is cooked and stir the contents of the pan around a bit. Put a lid on the frying pan and turn the heat down a little. Chop the basil up and when the pasta is ready (about 12 minutes after it starts to boil), turn off the heat under both pans and stir the basil into the sauce. You won't go wrong flinging on a bit of grated parmesan when you're serving up.