Preheat the oven to 350 degrees.
In a large mixing bowl, combine the softened butter, applesauce, eggs, sugar, and vanilla extract. Add in the almond flour, oat flour, baking powder, and salt. Combine until smooth.
Combine melted butter with oat flour, white sugar, and cinnamon evenly.
Add brown sugar, almond flour, oat flour, and cinnamon to the room temperature butter. Combine to form crumbly bits.
Grease or line an 8×8 baking dish. Pour half of the cake batter into the dish, sprinkle half of the cinnamon sugar filling on top, and swirl it into the batter. Add another layer of remaining batter followed by the rest of the cinnamon filling. Swirl again.
Bake for about 25 minutes until golden brown.
Remove from the oven and place the crumble topping on top of the cake. Press down gently.
Bake again for another 18 minutes until set.
Allow to cool completely before cutting into squares.