Preheat the oven to 190ºC (400ºF).
In a large mixing bowl combine egg with mashed banana, vegetable oil, vanilla extract and salt. Using a whisk or fork, stir the wet mixture for a couple of minutes until smooth.
Add the granulated sweetener of choice into the egg mixture and continue stirring until well combined.
Once smooth and lump free, mix in oat flour (and optionally protein powder), baking powder and baking soda. Stir to combine into a cookie dough, then fold in the chocolate chips.
Refrigerate the cookie dough for at least 15 minutes.
Scoop out some dough and shape the cookies. Transfer to a parchment paper covered baking sheet, spacing them apart.
Bake in hot oven for 8 to 12 minutes, do not overbake.