Heat olive oil in a large pot over medium heat. Add onions and garlic, and sauté for 2 minutes until onions are translucent.
Stir in carrots, celery, red and green bell peppers. Cook, stirring occasionally, until vegetables are slightly softened, about 5 minutes.
Add potatoes, diced tomatoes with juice, vegetable broth, and water. Stir in thyme, basil, Old Bay seasoning, salt, and pepper.
Bring to a boil over high heat, then reduce to a simmer. Cover the pot and let the soup simmer for about 20 minutes, or until potatoes are tender.
Stir in peas, corn, and green beans. Continue to simmer, uncovered, for an additional 10-15 minutes, until all vegetables are cooked through.
Adjust seasoning with more salt and pepper if needed. Serve hot, garnishing with fresh herbs if desired.