Preheat the oven to 200°C.
Pat-dry the chicken and put it in baking tray.
Combine the garlic with the lemon zest, cumin, coriander and the butter. Season with salt and pepper.
Rub the salt and pepper into the chicken’s cavity. Put the half onion in the cavity. Using your fingers, loosen the skin under the breasts and legs of the chicken. Rub the spiced butter under the skin coating as much of the breast and leg meat as you can.
Rub the outside of the chicken with the remaining paste.
Place the chicken breast-side down in the roasting tray and put it in the oven for 20 minutes.
Turn the chickens breast-side up, squeeze the lemon all over the chicken and stuff the lemon halves into the cavity of the chickens together with the fresh coriander.
Turn the oven down to 180C and roast the chicken for another 60-90 minutes, until golden and clear juice is running from the thighs (poke it with a skewer).
Rest for 10 minutes before carving.