Grease 2 9x4 inch loaf pans with butter or oil. Line the bottom with parchment.
Divide the dough in half. On a lightly floured surface, roll one half of the dough into a thin rectangle/square 10 inches wide and 10-12 inches long.
Spread half of the Nutella over the dough, leaving a 1/2 inch border around the edges. Sprinkle evenly with half of the chopped chocolate. Wet the 1/2 inch edge furthest from you with water. Starting with the edge closest to you, tightly roll up the dough, sealing the dampened edge. If desired, place the roll in the freezer for 10 minutes to Harden the chocolate slightly and allow the dough to be worked with more cleanly.
Slice off 1/2 inch off each end of the dough and discard. Slice the rope in half lengthwise and place on the work surface cut side up. Twist together the ropes, cut side facing out, end to end. You can also cross the ropes in the middle, then twist them to the ends starting from the middle.
Place the twisted loaf in the prepared pan and cover with a damp cloth. Repeat with remaining dough and filling. Allow to rise at room temperature until puffed, 1-2 hours.