2) Place a wire rack in a large roasting pan. Place the chicken, breast side up, on the rack in the pan. Put the chicken in the oven and roast for 1 hour, basting occasionally and adding some chicken stock to the pan, if necessary, to prevent the pan drippings from burning.
3) Whisk the orange juice, lemon juice, oil, oregano and chopped garlic in a medium bowl to blend. Brush some of the juice mixture over the chicken, after it has baked 1 hour. Continue roasting the chicken until an instant-read meat thermometer inserted into the innermost part of the thigh registers 77C, basting occasionally with the juice mixture and adding stock to the pan, about 45 minutes longer.
4) Transfer the chicken to a platter and tent with aluminium foil to keep warm while making the sauce (do not clean the pan). Place the same roasting pan over a medium-low heat. Whisk in any remaining stock and simmer until the sauce is reduced to 240ml, stirring often, about 3 minutes.
5) Strain the sauce into a 480ml glass measuring cup and discard the solids. Spoon the fat from the top of the sauce. Serve the chicken on a platter garnished with lemon slices, with the pan sauce in a separate jug to pour.