In a 4.5-qt. sauce pan, prepare a syrup by bringing to a boil the water, sugar and Grand Marnier.
Place the oranges in a medium bowl and pour the slightly cooled syrup over them. Allow to cool.
When ready to serve, slice the oranges into rounds and place on dessert plates and garnish with a bit of whipped cream. You may also serve whole in small bowls and drizzle with syrup and garnish with mint leaves.