Preheat the oven to 350°F and prepare a rectangular baking pan (the one used for loafs of bread): grease with a tablespoon of coconut oil, cover with wax paper and grease again. Set aside.
Mix all the dry ingredients in a bowl using a wooden spoon. Add the vegetable milk, vanilla extract, coconut oil, and ground flax seeds with water. Mix thoroughly. Finish by adding the mashed bananas in folding motion, and the blueberries. Pour the mixture into the baking pan and even the surface with a spatula.
As decoration, cut the banana into rondelles and put on top of the mixture with the blueberries. Sprinkle poppy seeds and bake for 40 minutes.