1 tablespoon olive oil
1 small onion (thinly sliced, about 1 cup)
1 tablespoon garlic (finely minced)
3 tablespoons tomato paste
6 cups fresh diced tomatoes (with juices or 2 28-oz cans diced or crushed tomatoes, with juice)
4 cups chicken stock
2 tablespoons chopped fresh basil
2 teaspoons dried oregano
  salt
2 ounces uncooked whole wheat thin spaghetti (broken into short 2-inch pieces, or about 1 cup cooked spaghetti)
12 ounces uncooked chicken or pork sausage (or cooked sausage)
  Freshly ground black pepper
  Grated parmesan cheese, as garnish (optional)