Combine water, lemon juice, onion, brown sugar, green onions, oil, salt, allspice, cinnamon, black pepper, thyme, and cayenne pepper in a blender or food processor. Blend until smooth. Reserve 1/2 cup for basting.
Place pork chops in shallow glass dish. Pour remaining marinade over the meat. Cover, and refrigerate at least 12 hours, but no longer than 24 hours.
Preheat grill for medium heat. Place grate 4 to 5 inches above heat source. Oil the grill grate. Arrange chops on grate, and discard marinade. Cover grill, and cook chops for 10 minutes, turning once, or to desired doneness.