Cook the onion in a little olive oil until soft. Add sliced turkey sausage and cook until browned. Add chicken broth, tortellini, tomatoes, salt and pepper. Bring to a boil, stirring often. Turn heat down to low, cover and simmer for about 15 minutes, or until pasta is cooked to al dente. Remove from heat and add cheeses, reserving a handful for topping. Cover and let stand for five to ten minutes. Grarnch with green onions, if desired. Serve hot.