Put your chicken in a pot large enough to completely cover it with water. Pour in cold water until it is completely submerged.
Half the lemons and onion (no need to peel). Add to the pot along with all of the other ingredients.
Cover with a lid or tin foil and put in the fridge for at least 12 hours, but ideally 24 hours.
When you are ready to roast, remove from the brine and cook as normal, minus 15 minutes (be sure to use a meat thermometer to make sure it is cooked through). Enjoy the tastiest, juiciest chicken!