Heat the oil in a large saucepan, add the garlic and saute for 3 minutes.
Add the chopped tomatoes, onions and half the parsley to the pan.
Fry gently for 10 minutes, stirring frequently.
Pour in the water, season with the salt and pepper and simmer, covered, for 20 minutes.
Raise the heat and drop in the pasta.
Cook, covered, for about 10 minutes, stirring occasionally, until the pasta is just cooked.
Just before serving, add the remaining parsley and garnish with the Parmesan cheese.