Cut all the vegetables (eggplant, zucchini, bell pepper, tomatoes, onions) so that they are approximately the same size and can cook evenly. Transfer them on a large rimmed baking tray. Add the garlic and herbs (thyme, bay leaves, and rosemary (optional). Sprinkle enough salt, pepper, and olive oil to enrobe them. Mix with your hands and spread them evenly on the baking sheet. It might seem crowded but they will shrink while cooking.