Activate the yeast by mixing it with warm milk and sugar, then let it sit until bubbly.
In a large mixing bowl, combine flour, cocoa powder, ground cinnamon, and salt.
Add the yeast mixture, melted butter, eggs, and vanilla to the dry mix, and knead until smooth.
Cover the dough and let it rise in a warm place until doubled in size, about 1 hour.
Punch down the dough and roll it out on a floured surface into a large rectangle.
Spread melted butter, sprinkle with sugar, cinnamon, and chocolate chips uniformly over the dough.
Roll the dough tightly into a log, then slice into equal pieces.
Place rolls in a greased baking dish and let rise again for about 30 minutes.
Preheat the oven to 375°F (190°C) while the rolls rise again.
Bake the rolls for 25-30 minutes or until golden brown and cooked through.
Allow the rolls to cool slightly, then mix the icing ingredients and drizzle over the top.