Cut the lemon in half and stuff it inside the cavity, along with half of the herbs. Place the chicken on the rotisserie spike and tight it firmly with the rotisserie hooks. Season with the rest of the herbs, salt and pepper.
Peel and rinse the root vegetables and cut them into chunks, turn them in oil, salt and pepper, and place in a drip pan.
At the barbecue:
Prepare the barbecue for indirect heat, approx. 180°C. If using a charcoal barbecue, you will need just half a chimney starter of lit briquettes.
Place an empty drip pan between the briquettes to collect fat and meat juices.
Fit the spit with the chicken into the rotisserie motor and leave to turn for approx. 30 min, with the lid on.
Replace the empty drip pan for the drip pan with root vegetables. Grill for another 45 minutes more.
Check the core temperature of the chicken – it must be 75 °C before the chicken is cooked through. Let the chicken stand for 15 minutes before carving and serve it with the root vegetables.