Brown sausage in half the olive oil and remove from pan. Sautee red onion in oil just until transparent. Return sausage to pan and add about 1 cup water. Bring to a boil then lower heat and simmer for about 10 minutes. In the meantime cook pasta to your taste. Strain paste and put back in pot, add sausage and mix. Plate, and have plenty of Italian cheese to top.
If you want it soupier just add pasta water and adjust salt and pepper.