Heat olive oil in a large pot over medium heat.
Add onion, carrots, and celery. Cook until softened, about 5 minutes.
Stir in garlic, zucchini, squash, and bell pepper. Cook for another 5 minutes.
Add diced tomatoes, vegetable broth, oregano, thyme, salt, and pepper. Bring to a boil.
Reduce heat and simmer for 20 minutes.
Add green beans and corn; simmer another 5-7 minutes.
Stir in spinach or kale and cook until wilted, about 2 minutes.
Adjust seasoning to taste and serve hot.