Preheat oven to 325°F (160°C). Line one large baking sheet with parchment paper and set it aside.
If you are using rolled oats, add the oats into a blender and blend for a few seconds. If you prefer a slightly rougher texture for your cookies, you can skip this step and simply use rolled oats in the recipe as they are.
Mash the banana. Chop the nuts and dark chocolate into small chunks.
Combine all of the ingredients into a large bowl and mix well until combined. The dough might seem quite dry, but don't be tempted to add water. For the best result, combine and mix the dough by hand.
Divide the dough into 12 balls.
With the palm of your hands, flatten the balls into a cookie shape. Whatever shape you give to the cookies, they will remain the same once cooked as this dough does not spread in the oven.
Put the cookies onto the baking sheet and bake for 12-14 minutes until the edges are slightly brown.
Once ready, let your breakfast cookies cool on a wire rack.
You can store them in an airtight container or in a jar at room temperature for up to 5 days. Or you can freeze them for up to a month.
Notes
Ideas for substitutions and alternatives: You can substitute rolled oats with steel-cut oats, and almond flour for coconut flour.And if you are not a banana fan, substitute it for a small freshly grated apple or even apple sauce. If you do, add an extra tablespoon of maple syrup.If you don't have chia seeds or flax seeds handy, you can simply leave them out.