Preheat the oven to 180°C (355°C).
Cut the leeks into lengths to fit your oven tray (or Dutch oven) and then cut in halves lengthways. Halve, core and deseed your peppers.
Coat the base of your oven tray with olive oil. Arrange the leeks in the tray and top with the peppers. Using a pastry brush, coat the vegetables with olive oil. Sprinkle over the chilli flakes, if using.
Top the vegetables with the chicken quarters, coat with olive oil and sprinkle with the sea salt flakes. Remove the thyme leaves from the stems and sprinkle half the thyme over the tray.
Place the olives and capers into the nooks and crannies on the and place the tray on the centre rack of the oven. Add the cracked pepper. Roast for 1/2 an hour then check for doneness. If the chicken is cooked through, but the skin is not browned, use the broiler element of the oven to brown up the skin.
When the chicken is ready, rest with the oven off for a few minutes before serving. Plate with the chicken quarter on one side of the plate and the vegetables on the other. Add the olives and capers from the tray and drizzle with the juices from the pan. Serve immediately.