Mix all of the dry ingredients in a pestle & mortar and then add in the Olive Oil & Natural Yoghurt and grind to a paste.
Spoon the mixture into a large sealable plastic cooking bag with the chicken and place the lemon in the cavity of the chicken. (This can be done the night before the BBQ to maximise marinating time!) Seal the bag and place into a large pan full of boiling water. Throw on the lid and leave to boil for 1-1 1/2 hours until the chicken is cooked.
Remove the chicken from the bag, saving any of the marinade in a separate bowl and place the chicken on a hot grill. Use the left over marinade to baste the chicken regularly. Cook until the chicken is lightly charred.