Whisk cream, 1 T sugar, and Grand Marnier in medium bowl to soft peaks; cover and chill.
Using vegetable peeler, remove peel from oranges in strips; add strips to medium saucepan Ireserve oranges for another use). Add milk; bring just to simmer over medium heat. Add chocolate, espresso powder, cocoa powder, and remaining 1 T sugar; bring just to summer, whisking to melt chocolate. Strain. ladle mocha into 4 mugs. Top with whipped cream.