Finely chop 2 sprigs of sage, then combine with lemon juice and olive oil into a bowl, season with salt & pepper.
Pour marinade over chicken, cover, and leave for 1 hour in the fridge.
Preheat oven to 180⁰C.
Place chicken into a roasting pan along with garlic & onions.
Add lemon halves and the remaining sage sprig into the cavity of the chicken.
Spoon a little of the chicken stock over the top and roast the chicken for approx. 1 hour or until cooked through and golden, basting regularly with the remaining stock.