Heat olive oil in a large pot or Dutch oven over medium heat. Add the chopped onion and cook for 5-7 minutes, or until softened and translucent. Stir in the minced garlic and cook for 1 more minute until fragrant.

Add the diced eggplant, zucchini, red bell pepper, and yellow bell pepper to the pot. Sauté for 10 minutes, stirring occasionally, until the vegetables begin to soften.

Pour in the crushed tomatoes and vegetable broth. Add the Herbs de Provence, salt, and pepper. Stir everything together, bring to a boil, then reduce the heat to low. Cover and let the soup simmer for at least 30 minutes to allow the flavors to meld.

For a thicker, more uniform texture, use an immersion blender to partially blend the soup. If you prefer a chunkier soup, you can skip this step entirely.

Remove the pot from the heat and stir in the fresh chopped basil. Taste and adjust salt and pepper if necessary. Serve hot.