Preheat the oven to 230°C. Layer the sliced vegetables on a roasting tray and add the garlic. Drizzle over 25 ml of the olive oil, season with salt and freshly ground pepper and toss together. Place the cod pieces in a ramekin dish, drizzle the remaining olive oil. Roast the vegetables in the oven for 20 mins and the cod for 10 mins. Remove and cool.
Transfer the roast vegetables over the cod in the ramekln dish, alternating the varieties and colours to produce a mille-feuille effect. Cover each ramekin with cling film, top with a weight and refrigerate for 2-3 hours. To serve, turn out each ramekin upside down onto a serving dish. Make sure you scoop out all the juices. Finish with a dressing made from the balsamic vinegar and a little olive oil.