Preheat the oven to 350°F. Grease an 8×8-inch baking pan or line with parchment.
Combine all of the topping ingredients in a small bowl with a fork until crumbly and set aside.
In a medium mixing bowl add flour, salt, cinnamon and baking soda and stir to combine.
In a large mixing bowl whisk together eggs, Greek yogurt, coconut oil, vanilla extract and maps syrup.
Add the flour mixture to the wet mixture and stir until just combined.
Gently fold in chopped apples.
Add cake batter to the prepared pan and sprinkle with the topping.
Bake for 40-50 minutes, or until a toothpick inserted into the center comes out clean, or with just a few moist crumbs sticking to it. Check the cake at the 30 minute mark to make sure the crumb topping isn’t browning too much. If it is you can cover the top with a piece of foil to prevent the top from burning.
Let cake cool for about 15-20 minutes before transferring to a wire rack to cool longer.
Once ready to enjoy, cut into squares and serve!
Store in an airtight container at room temperature for 2 days, in the fridge for 5-7 days or in the freezer for up to 3 months.