Wikipedia explains us the origin of this well known dish. Thus, Copy Paste :
The word ratatouille derives from the Occitan ratatolha and is related to the French ratouiller and tatouiller, expressive forms of the verb touiller, meaning “to stir up”. From the late 18th century, in French, it merely indicated a coarse stew. The modern ratatouille – tomatoes as a foundation for sautéed garlic, onions, zucchini, eggplant, bell peppers, marjoram, fennel and basil, or bay leaf and thyme, or a mix of green herbs like herbes de Provence – does not appear in print until c. 1930.
Do I have to add something in view of preparation? Pre-preparation of the eggplant in the oven can be useful. Pre-preparation of the bell peppers in the oven can be helpful to remove the skin (easier to digest for certain people). For 2p : 4 garlic cloves, 1 red onion, 1 bell pepper, 2 courgettes, 1 eggplant, 2 tomatoes of 1 small can of passata, 1 spicy little pepper, 1 teaspoon of dried basil, 1 teaspoon of dried oregan, 1 teaspoon of dried thyme, 1 bay leaf ,( and I love to add 1 teaspoon of cumin seeds) is a complete dish all together with oven baked chicken and some rice or couscous.
Doc V's Healthy Kitchen 