In a large pot, heat the olive oil over medium heat. Add the chopped onion and garlic, and sauté for about 3-4 minutes until the onion is translucent.
Add the diced carrot, celery, and green bell pepper to the pot. Cook for an additional 5 minutes, stirring occasionally.
Stir in the chopped cabbage and cook for another 3-4 minutes until it begins to wilt.
Pour in the diced tomatoes with their juice and the vegetable broth. Stir in the thyme, basil, salt, black pepper, and red pepper flakes if using.
Bring the mixture to a boil, then reduce the heat to low. Cover and simmer for 20 minutes.
Add the green beans and corn to the pot, and continue to simmer for another 10-15 minutes until the vegetables are tender.
Taste and adjust seasoning if necessary before serving.