Wipe the bird inside and out.
Heat the oven to 190˚C/170˚C fan/gas mark 5. Scatter the vegetables over the base of a roasting tin. Season the inside of the chicken liberally with salt and pepper, then stuff with the lemon halves and thyme.
Sit the chicken on the vegetables, rub all over with the oil, then season the outside with salt and pepper. Place in the oven and leave, undisturbed, for 1 hour 20 minutes.
To check if the chicken is cooked, pierce the thickest part of the breast with a skewer and the juices should run clear.
Allow the chicken to rest on a board for 10 minutes before serving.