Heat olive oil in a large pot over medium heat.
Add chopped onion and sauté until translucent, about 5 minutes.
Stir in minced garlic and cook for another minute.
Add sliced carrots and chopped celery; cook for 5 minutes.
Incorporate diced bell pepper and zucchini, stirring to combine.
Add green beans and cook for another 3-4 minutes.
Pour in vegetable broth and diced tomatoes.
Season with oregano, salt, and pepper.
Bring the soup to a boil, then reduce heat to a simmer.
Cover and let simmer for 20 minutes until vegetables are tender.