Preheat the oven to 375 degrees. Prepare two large baking sheets with parchment paper or nonstick cooking spray.
Place 1 cup oats into a food processor or blender and pulse until the oats are ground into oat flour.
In a large bowl, whisk together 1 cup of whole oats, oat flour, baking soda, cinnamon, nutmeg, salt, and flax.
In a medium bowl, whisk together the butter, maple syrup, egg, and vanilla. Combine the wet ingredients with the dry ingredients.
Stir in the bananas and walnuts.
Using a large scoop, divide the dough into 32 cookies. Press the tops flat as these cookies remain in the same shape as they cook.
Bake for 10 minutes or until the middle is set. Allow to cool on the baking sheet for 10 minutes before transferring to a wire rack.