First of all preheat the oven to 180C and prepare your muffin tin by lining 12 hole muffin tin with paper muffin cases.
Combine all the dry ingredients (apart from the chocolate chips) together in a bowl.
Combine all the wet ingredients (apart from the bananas) in a mixing jug.
Mash the bananas with fork, but don't over mash it. I like to keep few chunks of bananas unmashed.
Gently stir the wet ingredients into the dry ingredients, but don't overmix it.
Stir in the bananas and chocolate chips.
Spoon the muffin mixture into the muffin cases and divide equally between the cases.
Topp up each muffin mixture with Nutella and swirl it in. You can also add the Nutella inside the muffin as you add it to the tin (which is what I did with mine)
Bake in preheated oven for about 20 minutes or until it's golden brown. Check with a wooden skewer to make sure the muffins are baked.
Cool on a cooling rack