In a small saucepan, combine the water, honey, and sugar. Heat over low heat, stirring constantly, until melted and smooth. Remove from heat and let cool to room temperature.
Pulse the candied lemon and orange peel in a food processor until very fine.
Add the candied peel, lemon zest, cocoa powder, lebkuchen spice, and cinnamon to the cooled honey mixture. Mix with a hand or stand mixer until well combined.
In a separate bowl, combine the ground nuts, baking powder, baking soda, and flour. Gradually add the flour mixture to the honey mixture and knead until a thick dough forms. Add the milk in small portions as needed to make kneading easier.
Wrap the dough in plastic wrap or place in an airtight container. Let rest at room temperature overnight.
The next day, preheat your oven to 180°C (350°F) and line a large baking sheet with parchment paper.
Form the dough into approximately 2 cm (¾ inch) wide logs and place onto the baking sheet.
Bake for about 15 minutes.
Meanwhile, make the icing. Melt the chocolate and butter in a double boiler, then carefully sieve in the powdered sugar until you get a nice thick icing.
Once removed from the oven, cut the gingerbread immediately while still soft. Cut diagonally for the traditional diamond sshape (Rautenform). Coat each piece in the icing and leave to set.