Grease a large ovenproof baking/casserole dish with a little olive oil. Set aside.
Slice the onions. Heat 1 tablespoon of olive oil in a frying pan and saute the onions until soft. Add the slices garlic and fry for a further minute, then spread over the bottom of the baking/casserole dish.
Slice all the other vegetables into slices 0.5-1cm wide, depending on your own personal preference. Heat the oven to 180C fan/400F.
Lay the vegetables in rows, starting with the peppers, then tomatoes, aubergine, and courgette. Repeat until you have used up all the vegetables.
Drizzle over the remaining olive oil, and thyme. Season with salt and pepper.
Bake for 15 minutes (uncovered) then turn down the oven to 160C fan/350F and cook for a further 45 minutes to an hour (still uncovered). Serve hot or in the classic style at room temperature.