Preheat the oven to 350°F (180°C/Gas mark 4).
Roll out the puff pastry thinly into a rectangle about 1/8 inch (3 mm) thick. Drape the pastry over the rolling pin and unroll it onto a baking sheet.
Place a wire cake rack on top and bake the pastry for
about 15 minutes or until golden brown.
Allow to cool a little, then cut into four 4 in. (10 cm) rounds using a plain pastry cutter.
Peel and finely chop the onions and sweat them in a pan in a little olive oil.
Season with salt and pepper and then cover the pan and stew the onions for 45 minutes.
Drain through a sieve to remove excess oil. Reserve.
Preheat the oven to 300°F (150°C/Gas mark 2).
Wash all the remaining vegetables.
Brush the bell peppers with olive oil and season. Lay on a baking sheet and cook in the oven for 1 hour.
Meanwhile, remove the stalks from the tomatoes and cut a cross with a small knife in the base of each tomato to make them easier to peel.
Immerse in boiling water for a few seconds and then in cold water.
Slip off the skins, quarter the tomatoes, remove the cores and seeds, and discard.
Oil a baking sheet and lay the tomato quarters on it.
Slice the eggplant and zucchini lengthways, leaving the skin on.
Add the slices to the baking sheet with the tomatoes on it, spreading the vegetables out in a single layer.
Season with salt and pepper and cook in the oven for 45 minutes.
When the vegetables are cooked, cut them into even-sized rounds using a 1 in. (2.5 cm) plain pastry cutter.
Spread the stewed onions over the pastry rounds and arrange the vegetables in overlapping rings on top.
Make small bouquets with a few sprigs of basil and thyme and place in the center of the ratatouille “galettes.”
Serve cold and drizzle with olive oil just before serving.