Heat olive oil in a large pan over medium heat.
Add the chopped onion and cook until softened, about 5 minutes.
Stir in the minced garlic and cook for another minute.
Add the diced bell pepper, zucchini, and eggplant. Cook, stirring occasionally, until the vegetables start to soften, about 10 minutes.
Stir in the chopped tomatoes and tomato paste. Mix well.
Add the black olives, capers, dried oregano, dried basil, and bay leaf. Season with salt and pepper to taste.
Simmer the mixture for about 20-30 minutes, or until the vegetables are tender and the flavors are well combined.
Remove the bay leaf before serving.
Garnish with chopped fresh basil or parsley, if desired.
Enjoy your meal!