Heat olive oil in a large pot over medium heat. Sauté onions, celery, and carrots until tender (about 5 minutes).

Add minced garlic and cook for an additional minute.

Stir in diced tomatoes and drained cannellini beans.

Pour in vegetable broth and add dried oregano. Bring to a gentle boil.

Lower the heat and let it simmer uncovered for 20 minutes.

In the last few minutes of cooking, add fresh spinach until wilted.

Serve hot, drizzled with olive oil or topped with grated Parmesan if desired.