1. In large pot, heat oil over medium heat. Add onion and cook until soft. Add garlic and cook about 1 minute.
2. Stir in carrots and celery. Reduce heat to low, cover and cook 12-15 mins, or until softened.
3. Stir in vegetable stock, tomatoes with juices, basil and vinegar and bring to a boil. Reduce heat and simmer, uncovered, for 10 mins.
4. Stir in salt, pepper and green onions and simmer, uncovered, for another 30 minutes or until soup reaches desired thickness.