Preheat the oven to 200°C/ 400°F/Gas 6. Rub the chicken all over with olive oil and season with pepper.
Place the lemon half inside the bird, with a sprig or two of thyme. Put the chicken breast side down in a large roasting pan. Roast for about 30 minutes.
Remove the chicken from the oven and season with salt. Turn the chicken right side up, and baste with the juices from the pan.
Surround the bird with the potatoes, roll them in the pan juices, and return the roasting pan to the oven, to continue roasting.
After 30 minutes, add the aubergine, red pepper, fennel and garlic cloves to the pan. Drizzle with the remaining oil, and season with salt and pepper.
Add any remaining thyme to the vegetables. Return to the oven, and cook for 30-50 minutes more, basting and turning the vegetables occasionally.
To find out if the chicken is cooked, push the tip of a sharp knife between the thigh and breast. If the juices run clear, it is done. The vegetables should be tender and just beginning to brown.
Serve the chicken and vegetables from the pan, or transfer the vegetables to a serving dish, joint the chicken and place it on top. Serve the skimmed juices in a gravy boat.