Preheat oven: Preheat the oven to 350°F. Line an 8 x 8 square baking pan with parchment paper.
Make flaxseed egg: combine ground flax with water. Let sit up for 5-10 minutes.
Mix wet ingredients: Mix together flaxseed egg, yogurt, coconut oil, coconut sugar and vanilla.
Mix dry ingredients: In a separate bowl, mix together the flour, baking powder, baking soda, cinnamon and salt.
Combine: Add the flour mixture to the wet mixture.
Make topping: Combine all of the topping ingredients.
Add to pan: Add cake batter to the prepared pan and sprinkle with the cinnamon sugar topping.
Bake: Bake the coffee cake for 30 to 35 minutes, or until a toothpick inserted into the center comes out clean, or with just a few moist crumbs sticking to it.
Serve: Serve the cake warm or at room temperature. Wrap the completely cooled cake airtight, and store at room temperature for several days; freeze for longer storage.