Heat olive oil in a large skillet over medium heat.
Add the chopped onion and garlic, sautéing until translucent.
Stir in the diced eggplant and cook for about 5 minutes.
Add the zucchini and bell pepper, cooking until soft.
Mix in the diced tomatoes and thyme.
Season with salt and pepper to taste.
Reduce heat and let it simmer for 30 minutes, stirring occasionally.
Check for seasoning and adjust as necessary.
Remove from heat and allow to cool slightly.
Garnish with fresh basil before serving.