1. Cut the aubergine, the tomatoes and the courgettes into cubes, without peeling them. De-seed the peppers and cut them into cubes. Slice the onion and chop the garlic.
2. Heat the oil in the casserole dish and brown the onions for 5 minutes. Add all the vegetables, the garlic and the herbes de Provence. Salt and pepper. Stir.
3. Cover and simmer for 15 minutes.
4. During this time, place the sole filets on the work surface. Place a mushroom and an olive in the center of each one, roll the filets up and secure them with the help of a cocktail stick. Place the sole rolls in the steam basket. Salt and pepper.
5. When the 15 minutes cooking time for the ratatouille is up, place the steam basket on the casserole dish. Cover and simmer for 20 minutes.