Heat the oil in a frying-pan over a medium heat and sweat the garlic for a few minutes until soft and starting to caramelize. Add the tomatoes, half of the basil and a pinch of sugar. Season with salt and the oregano. Simmer over a gentle heat for at least 15 minutes. Cook the spaghetti in a large saucepan of slightly salted boiling water until al dente. Drain and mix with the sauce. Sprinkle the remaining basil over the top and serve immediately.