In a saucepan, combine pineapple and syrup with sugar and cinnamon. Simmer until the liquid is reduced to 2 or 3 tablespoons. Strain pineapple, reserving syrup in one bowl and pineapple in another. Thoroughly chill both in the refrigerator.
Place macadamia nuts in a nonstick pan and toast over medium heat for 3 or 4 minutes, or until lightly browned, stirring frequently. Transfer nuts to a bowl and cool to room temperature.
Line a 4-cup ring mold with plastic wrap and place in the freezer for 5 minutes. (A 4-cup bowl or cake pan can be used if you do not have a ring mold.) Allow the ice cream to soften for a 4 or 5 minutes outside the freezer. Then spoon two-thirds of the ice cream into the mold, pressing against the sides and bottom of the pan, entirely covering the internal surface and creating a channel for adding the other ingredients. Return mold and ice cream to freezer for 1 hour.
Set aside 1/4 cup of the pineapple for decoration. Combine remaining pineapple, nuts and, if used, marshmallows and ginger. Spoon mixture into the channel of the ice cream mold. Press the ingredients into the ice cream, thoroughly packing the mold. Press the remaining ice cream over the top of the mixture. Place in the freezer for 3 hours.
Unmold the ice cream by setting mold into a shallow pan of warm water for about 15 seconds. Invert ice cream onto a plate and return to the freezer for 45 minutes.
Remove from freezer and drizzle surface with pineapple syrup. Press coconut onto the surface and garnish with the reserved pineapple tidbits.
Return to freezer until ready to serve. If not serving within 1 hour, cover the ice cream with plastic wrap.
The dessert is best when not made more than 10 hours before serving.
