Heat olive oil in a large pot over medium heat.
Add the diced onion and cook until translucent, about 5 minutes.
Stir in the minced garlic and cook for another minute.
Add the diced bell pepper, zucchini, and eggplant; sauté for about 7 minutes.
Mix in the chopped tomatoes and cook for 3 more minutes.
Pour in the vegetable broth, then stir in thyme, salt, and pepper.
Bring the mixture to a boil, then reduce the heat and simmer uncovered for 20 minutes.
Taste and adjust seasoning if necessary, then serve.