1. Preheat oven to 180°C (or gas mark 4), and lightly oil a 28 x 18 centimetre pan.
2. Add oats to a food processor, and grind into flour.
3. Add the bananas, almond butter, and cocoa powder, and mix until a smooth batter forms.
4. Spread the batter evenly into the pan using a spatula and top with chopped walnuts.
5. Bake for 15 minutes or until a toothpick inserted comes out clean.
6. Cool slightly before cutting into eight squares. Enjoy! Store leftovers in an airtight container or freeze.

Here's the nutritional information for one brownie: