To the mashed bananas in a bowl, add melted butter, and mix it thoroughly. Add organic coconut sugar and mix again.
Add eggs and vanilla extract and mix once again.
Using a sieve, sift whole wheat flour, baking soda, salt and ground cinnamon, and add to the wet ingredients mixture. Using a spatula, fold gently till all ingredients form a homogeneous mixture (Do not over-mix at this stage).
Grease and dust the muffin pan. Preheat oven to 350 degree Fahrenheit (or 180 degree Celsius). Pour batter into greased (or lined) muffin cups.
Add half a tablespoon of Nutella over the muffin batter in each muffin cup. Then, use a toothpick to gently swirl Nutella over the batter.
Bake the muffins in preheated oven for 25 minutes or till done (when the inserted toothpick comes out clean).
The Banana Nutella Muffins are ready to be served warm, or these can be stored in an airtight container in the refrigerator for a week!