Preheat oven to 375°F, Lightly oil or butter a 9" square baking pan.
Place the four streusel ingredients into a bowl and mash together with the back of as fork. You should leave it a little lumpy.
Mix the chia seed or flax seed meal together with the water and set aside to gel.
To a large bowl add the flour, sugar, baking powder, salt, dairy free butter and milk, vanilla, and chia seed mixture. Mix until well combined.
Pour into the prepared pan and spread evenly.
Prepare the apple, peeled and grated or diced. This is done at the last minute to keep the apple from turning brown.
Sprinkle the apple evenly over the batter mixture.
Evenly spread the streusel mixture over the top of the apple.
Bake at 375° for 40 to 45 minutes or until a toothpick comes out clean after inserting in the center of the cake. Remove from oven and let cool for 10 minutes.