In a large saucepan, heat olive oil and butter over medium heat. Add onions and cook, stirring often, until softened, about 6 to 7 minutes. Add garlic and cook for 1 minute longer. Add eggplant and stir to coat with the oil and butter. Add peppers; stir to combine. Cover and cook for 10 minutes, stirring frequently to keep vegetables from sticking.
Add the tomatoes, zucchini, and herbs; mix to blend. Cover and cook over low heat about 15 minutes, or until eggplant is tender but not too soft. Taste and add salt and pepper, as needed.