Preheat oven to 350˚F. Line a baking sheet with parchment paper or a silicone pad.
In a high power blender or food processor, pulse the oats a few times until you get a rough flour consistency.
Pour oats into mixing bowl and add cacao powder, baking soda and spices.
Mash bananas with a fork until completely smooth. Add to oatmeal mixture along with vanilla. Blend well with a spatula.
Add nuts and mix until combined.
Using an ice cream/cookie scoop (= about 2 tbsp), drop balls of dough onto cookies sheet, spacing well. With lightly moistened fingers, flatten the balls slightly.
Bake 20 minutes. Cool on the sheet pan 15 minutes then on a wire rack until completely cool.
Store in an airtight container
Notes
Option: you can add 1/4 cup of raisins with the walnuts. Recipe makes 16 cookies then, and nutritional value becomes 114 calories per cookie.