Start by preheating your oven to 160°C and line a rimmed baking sheet or large baking dish with parchment paper.
Mash the bananas and mix them with the eggs, oil and vanilla extract.
Add the ground hazelnuts and baking powder and stir until well combined.
Beat the egg whites with a pinch of salt until stiff. Then carefully fold the beaten egg whites into the batter.
Pour the batter into the prepared dish and sprinkle the chocolate chips on top, if using. Then bake in the middle of the oven for ca. 30-35 minutes.
Let cool completely before cutting into squares.
*You can use other oils for the hazelnut oil.
**If you can't find ground hazelnuts at the store, simply make it yourself. Put in a high power blender or food processor and process until it becomes a flour. But be careful not to process too long, as once the oils are set free, it becomes a paste (hazelnut butter). Tasty, but not what you want right now.