Soak eight wooden skewers in cold water for 30 minutes to stop them from burning during cooking.
Slash each chicken half a few times to allow the marinade flavours to penetrate.
Run a wooden skewer through the flesh of each chicken piece to secure to the joints, and place in a large baking dish.
Place the coriander, peppercorns, salt, garlic, lime juice and oil in a blender or food processor and process until smooth.
Pour the marinade over the chicken pieces, rubbing well into the flesh, and cover with plastic wrap.
Place in the refrigerator to marinate for 2 hours, bringing to room temperature in the last 30 minutes.
Preheat the barbecue to high.
Place the chicken halves on the barbecue and cook, cut-side down, for 6 to 8 minutes.
Turn and cook flesh-side down for a further 5 to 6 minutes, or until the chicken is cooked through.
Alternatively, preheat the oven to 220°C (425°F/Gas 7).
Place the chicken on a baking tray, skin-side up, and bake for 30 to 35 minutes.
Garnish with coriander sprigs and serve with the cucumber relish and lime cheeks.
NB: Remove the backbone from the chicken by cutting either side of the bone. Flatten out chicken with the palm of your hand, and remove the breastbone by cutting on either side of the bone. Skewer to secure the joints.
Place the vinegar and sugar in a small saucepan over a medium heat, and stir until the sugar has dissolved.
Remove from the heat and cool.
Pour into a bowl, add the cucumber, shallots and chilli and stir to combine.