Preheat oven to 350°F (175°C). Grease or line an 8-inch cake pan.
- Pulse rolled oats in a food processor or blender until they reach a flour-like consistency.
- In a bowl, combine oat flour, cocoa powder, baking powder, baking soda, and salt.
- In another bowl, whisk mashed bananas, eggs, honey, yogurt, vanilla extract, and milk until smooth.
- Gradually add dry ingredients to wet ingredients, stirring until just combined. Fold in chocolate chips if using.
- Pour batter into the prepared pan and bake for 30-35 minutes or until a toothpick inserted in the center comes out clean.
- Let cake cool for 10 minutes in the pan, then transfer to a wire rack to cool completely before serving.