Remove the top and bottom of the pineapple. Quarter the pineapple lengthwise, remove the core, cut along husk to separate the meat then cut the meat into 1/2-in (1.27 cm) slices. Keep the slices on top of the husk, place the husk quarters husk down on a preheated grill. Grill on MEDIUM for 15 minutes, or until heated through. Combine the syrup, cinnamon and Grand Marnier in a small bowl, baste the pineapple with this mixture every 5 minutes for a sweet sticky delicious finish.