Grease a large mixing bowl with oil. Set aside.
In a small bowl, combine water, the yeast, and 2 teaspoons of the sugar. Let stand 10 minutes til it's foamy.
In a medium saucepan, combine the milk, remaining sugar, salt, and butter. Stir occasionally over medium heat. For best results use an instant read thermometer and heat til mixture reaches between 120-130 degrees Fahrenheit.
In a stand mixer fitted with the paddle attachment, mix til combined 2 cups of flour, the egg, egg yolk, milk mixture and yeast mixture. stir together the flour, salt and remaining sugar. Change the paddle attachment out for the dough hook.
With the mixer on low speed, add flour 1/2 cup at a time. Mix on low speed until the dough starts to pull away from the sides of the bowl and starts to form a ball around the hook. Remove dough from the bowl. Knead it on a lightly floured surface til smooth and elastic (about 9 minutes).
Place dough in the large oiled bowl. Turn dough over once to coat. Cover with a clean kitchen towel. Set bowl in a warm, draft free spot for 1 hour or til doubled in size.
Chop banana into small pieces.
Turn the dough out onto a lightly floured suface. Use a rolling pin to roll the dough out to a 1/4 inch thick rectangle (about a 16 by 12 inch rectangle).
Spread the Nutella evenly. Leave a 1/4 inch border on all sides. Sprinkle the cinnamon and finely chopped banana (if using) evenly on top.
Starting on the long side closest to use, tightly roll dough away from you into a log. Place the dough seem side down and put your hands on each end of the log. Push the ends gently towards the middle to compact the log a bit.
Slide an 11 inch string of unflavored dental floss (or thin sewing thread) under the roll. Hold the two ends up and cross them over the log. Pull through to cut. Cut off 1/2 inch to 1 inch off both ends. Discard those uneven end pieces then slice the rest of the log into 12 equal pieces.
Place rolls in a 9 x 13 inch rectangular dish lined with parchment paper and lightly sprayed with baking spray. Cover with a clean kitchen towel or plastic wrap and let rise for 30-45 minutes. Preheat oven to 350 degrees Fahrenheit.
Bake at 350 for 25-30 minutes until rolls are lightly golden brown. Remove from oven and allow to cool.