Pour olive oil into a large pot over high heat. Add onions and garlic and sauté for 2 minutes. Reduce heat and add tomatoes, eggplants, zucchini, tomato purée, and herbes de Provence; season with salt and pepper. Cover and simmer for 30 minutes.
Uncover and check the level of liquid in the pot. Continue cooking for 30 minutes, uncovered if there is too much liquid or covered if the amount of liquid looks right.
