Preheat oven to 350F. Line an 8x8 cake pan with parchment paper.
Stir together the ground flaxseed with 4 tablespoons of water in a small dish. Set aside to thicken. This is our egg replacement.
Whisk together the gluten-free all-purpose flour, almond flour, baking powder, baking soda, salt, and the spices in a large bowl until well combined.
In a separate bowl, whisk together the applesauce, vegan yogurt, apple cider vinegar, olive oil, flaxseed mixture, and brown sugar until well combined.
Pour the wet batter into the dry ingredients and fold to mix until just combined or you don't see any streaks of flour. Avoid over-mixing.
Make the apple topping by mixing together the brown sugar, flour, chopped pecans, cinnamon, salt and melted vegan butter until crumbly. If the mixture is too wet, add a tablespoon more flour. Chop the apple and stir into the topping mixture.
Pour the cake batter into the prepared pan and then sprinkle the apple brown sugar crumble evenly over the top.
Bake for 40-45 minutes or until a toothpick comes out clean.