Dry roast the rolled oats in a pan on low heat for two minutes. Cool for 3-4 minutes and then grind it in a mixer at high speed into a fine powder.
Preheat Oven to 350F or 180 degrees Celsius. Line a brownie pan with parchment paper or if using an aluminium foil, grease it with cooking spray or oil.
Sieve the powdered oats flour and measure ½ cup. Add baking powder, baking soda and salt into the fine oats flour and mix it evenly.
Mash the banana in a bowl using a fork. Add the flaxseed meal in about 3 tbsp of lukewarm water. Stir and mix till it is frothy.
In a large bowl, beat sugar, oil and the flax seed mixture using an electric mixer for about 2 minutes.
Add vanilla extract and cocoa powder and beat it at low speed till you get a smooth and creamy mixture. Do not over beat.
Add mashed bananas and flour into the bowl.
Add the chopped walnuts and chocolate chips into it. Stir and mix well so the oats flour is well incorporated.
Grease the baking pan and dust with flour. Tap off the excess flour.
Pour the batter into the prepared pan and bake for 35-40 minutes. When done, the edges of the brownies will be visibly baked through and the center will be set (that is, not wiggly) when you shake the pan.
Try to look for the first sign of cracking on the brownie’s top—which should be shiny and set which means that the brownies are cooked and then pull them out.
Cool down the brownies completely in the pan on a wire. After the brownies are completely cooled, after an hour, cut them into neat squares.