Cut zucchini, eggplants, potatoes, peppers and onions into thin slices and season with salt and pepper. Place the vegetable slices alternately in layers, starting from the periphery and moving to the centre until the pot is filled. Sprinkle with olive oil. Place in hot oven (190°C) for 15 minutes to soften slightly.
Dilute a jar of smoked sweet tomato sauce with a little water and pour over the food. You can add some ripe cherry tomatoes to fill the gaps between the vegetables. Cover the pot and put it in the oven for about 1 hour or until the ratatouille has little liquid and the vegetables are cooked.