Heat vegetable oil in a large cast-iron saucepan (cauldron), add onion and celery, fry, stirring occasionally, for about 3 minutes, then add broth, add corn, carrots, beans, potatoes, basil, thyme and green onions, bring to a boil.
Reduce heat, cover pot and cook soup for 10-15 minutes, until potatoes are soft.
Put chopped tomatoes and tortellini in a saucepan with soup, cook, uncovered, for 4-5 minutes, until tortellini is done.