First of all, prepare the flax egg. Add 2 tbsp flaxseed powder in 6 tbsp water and keep aside for 5 minutes undisturbed. Meanwhile, prepare for the batter.
In a mixing bowl add whole wheat flour, baking soda, salt, and cinnamon powder. Sift 2-3 times so that flour becomes airy and combines with every ingredient very well.
Furthermore, prepare walnuts and preheating oven. Add roasted walnut in a small bowl with 1 tbsp of flour and toss it. Doing so walnuts will not sink in the batter.
Preheat the oven at 350 F or 180C for 5 minutes. Grease a baking sheet pan and keep it ready. I used 7×11 inch pan.
Take another mixing bowl and add olive oil, coconut sugar, flax egg, and banana puree. Whisk nicely and should be a consistent mixture.
Finally, mix dry ingredients to wet ingredients. Do not mix all flour in one go, add one part and combine well, and so on till all dry flour gets over.
Pour the batter in the greased pan and bake for 30 minutes. At 25 minutes completion do check with the toothpick if it comes out clean.
After the baking done, let the eggless banana sheet cake cools down to room temperature completely. I left it overnight before frosting.
Take the chilled coconut cream in a bowl, use the thick part, discard the liquid part. Add sugar and maple syrup. Beat with the electric mixer till sugar dissolve. It will not be like normal whipped cream. It has a soft peak.
Spread it over the sheet cake and sprinkle some chopped walnuts. Best banana walnut cake or Vegan banana walnut cake is ready to serve.