In a large saucepan, heat oil over medium heat. Add the onion and sausages. Using a wooden spatula, break up the sausages into small pieces. Cook for about 10 minutes, stirring a few times.
Add garlic and cook for 1 minute.
Add the crushed tomatoes, vegetable broth, basil, crushed chili, salt and pepper. Bring to a boil. Reduce heat and simmer for 25 minutes.
Add the tortellini and cook according to the cooking time on the package.