Preheat oven 350℉ (177 degrees C). Put an 8x8 baking pan with parchment paper and lightly grease, then set aside.
Mix all the dry ingredients, such as oat flour, almond flour, ground flaxseeds, baking powder, cinnamon, and salt, in a large bowl and set it aside.
In a medium bowl, add maple syrup, almond milk, and vanilla, stirring until thoroughly combined.
Fold in walnuts, raisins, and apples together with wet ingredients.
Now make a hole inside the dry ingredients and add the apple mixture. Stir with a spatula or spoon well until you have a smooth and thick apple batter.
Pour the batter into the prepared pan and bake for 40-45 minutes, or until a fork or toothpick inserted in the cake's middle comes out clean.
After the cake is prepared, let it cool for 20 minutes before taking it out from the pan.