Sugared Walnuts: In a deep saucepan, combine the sugar, water, orange zest and cinnamon and bring to a boil. Add the walnuts and simmer, stirring, as the water evaporates. The glaze will be shiny and transparent at first, then turn opaque as the water cooks away. When the nuts are completely coated with sugar crystals, they are done. Spread them out on a sheet pan to cool. (To wash the saucepan, soak it overnight.) The walnuts can be made up to 2 weeks in advance and stored in an airtight container.
Sundae Cups: Spread the toasted walnuts out on a plate. Dip the rims of 6 coffee cups or mugs into the melted chocolate, then into the chopped walnuts. Turn them right side up and set aside. Dip 6 teaspoons in the chocolate and sprinkle with chopped walnuts. Let the cups and spoons cool at room temperature until set, about 2 hours. The cups can be made up to 2 days in advance.
To assemble sundae, scoop ice cream into each chocolate-dipped coffee cup and pour espresso over it. Top with a dollop of whipped cream and sugared walnuts. Place the cup on the saucer and rest a chocolate-dipped spoon alongside.