Combine water, lemon juice, onion, dark brown soft sugar, spring onions, oil, salt, allspice, cinnamon, black pepper, thyme and cayenne pepper in a blender or food processor. Blend until smooth. Reserve 125ml for basting.
Place pork chops in shallow glass dish. Pour remaining marinade over the chops. Cover, and refrigerate at least 12 hours, but no longer than 24 hours.
Preheat barbecue for medium heat. Place grate approximately 12cm above heat source.
Oil the barbecue grate. Arrange chops on grate and discard marinade. Cover barbecue and cook chops for 10 minutes, turning once, or to desired doneness.