Grind and bash all the spiced rub ingredients in a pestle and mortar until fine (or use a blender or coffee grinder). You can use the spices as a dry rub, or muddle in 2 tablespoons each of olive oil and red wine vinegar to make a marinade. Use a fork to pierce the underside of the chicken a few times, going all the way down to the bone (this will help create big flavour). Toss the chicken in the spiced rub or marinade, then cover and place in the fridge for at least 30 minutes, preferably overnight. Place all of the sauce ingredients into a medium saucepan over a high heat (you can do this on the hob or by placing a small pan on the direct side of the barbecue). Add a pinch of sea salt, whisk well to combine, then bring to the boil. Reduce the heat to low and simmer for 10 to 15 minutes, or until it's sticky and coats the back of a spoon. Remove from the heat and allow it to cool slightly. Once you’re ready to cook, preheat your barbecue (see tip). Place the chicken skin-side down on the direct or hot side of the barbecue and cook for 2 minutes, calming down any flames by putting the lid on. Using tongs, carefully turn the chicken over and transfer to the cooler part of the barbecue, where the indirect heat is (if you want to add some water-soaked fruit woods, such as Applewood, to the coals for bonus flavour, now’s the time to do it). Place the lid on (the holes in the lid should be open to allow the air to flow through), and cook for 25 to 30 minutes, checking and turning the chicken throughout, or until the chicken pulls easily away from the bone. When removing the lid, just crack it open slightly before lifting it off completely – this will prevent the ash from blowing up onto the chicken and tainting the flavour. Baste the chicken in half the BBQ sauce (save the rest for another day), place back over the indirect heat and pop the lid back on for 10 minutes, or until sticky, juicy and gnarly. Check the chicken is cooked through and the juices run clear, then transfer to a large serving board or platter. If using, finely chop and scatter over the fresh chilli and slice the lemon into wedges for squeezing over. Delicious served with a seasonal salad or barbecued vegetables, rice and flatbreads.