In a large pot, heat the olive oil over medium heat. Add the diced onion and sauté for about 5 minutes until it becomes translucent.
Stir in the minced garlic and cook for an additional 1 minute until fragrant.
Add the zucchini, yellow squash, eggplant, and red bell pepper to the pot. Cook for about 8-10 minutes, stirring occasionally, until the vegetables are slightly softened.
Pour in the diced tomatoes with their juices and the vegetable broth. Stir in the dried basil, dried oregano, salt, and pepper.
Bring the mixture to a boil, then reduce the heat and let it simmer for 20-25 minutes, allowing the flavors to meld and the vegetables to become tender.
Taste and adjust seasoning if necessary. Serve hot, garnished with fresh basil leaves if desired.