Preheat the oven to 350 °F (180 °C).
Line a large cookie sheet with parchment paper. Slightly oil paper with cooking oil spray. Set aside.
Mash the bananas and pack it in a ¾ cup measuring cup to measure precisely.
In a large mixing bowl, combine all the ingredients: mashed banana, peanut butter, oats, and flaxmeal. Stir in the optional vanilla extract, salt, cinnamon, or coconut sugar now. Stir until fully combined and a sticky cookie dough forms.
Stir in optional chopped nuts or chocolate chips. Combine until it is well incorporated.
Use a cookie dough scoop to form 8 cookie dough balls. The dough is sticky and that's normal. Lightly oil the back of a fork and press down the cookie dough balls slightly to form a round cookie shape.
Place each ball onto the prepared baking tray, leaving a 1-thumb space between each of them. They won't extend in the oven, the shape you give now, is the shape you get after baking.
Bake the cookies for 16-18 minutes at 350 °F (180 °C) until golden brown.
Let the cookies cool on the cookie sheet for 15 minutes, then transfer them to a cooling rack for 30 minutes.
