Preheat the Oven: Preheat your oven to 180°C (360°F) to get it ready for baking.

Mix Dry Ingredients: In a large bowl, combine oatmeal, cocoa powder, chopped walnuts, vanilla sugar, ground almonds, and oat flakes. Mix well to evenly combine.

Add Wet Ingredients: Add the mashed banana and water to the dry mixture. Stir thoroughly until all ingredients are well combined into a sticky dough.

Prepare the Baking Sheet: Line a baking sheet with parchment paper or lightly grease it with oil to prevent sticking.

Shape the Cookies: Scoop tablespoons of the mixture onto the prepared baking sheet. Flatten each scoop slightly with the back of a spoon to shape the cookies.

Bake: Place the baking sheet in the preheated oven and bake for 12-15 minutes, or until the cookies are set and a toothpick inserted into the center comes out clean.

Cool and Serve: Allow the cookies to cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.