Preheat the oven to 350°F and line a large baking sheet with parchment paper.

In a small bowl, combine the flaxseed and warm water and set aside to thicken for 5 minutes.

In a large bowl, stir together the oat flour, the additional 1 cup rolled oats, almond flour, lemon zest, baking powder, baking soda, cinnamon, and salt.

In a medium bowl, combine the almond butter, coconut oil, and maple syrup and stir well to incorporate. Stir in the flaxseed mixture.

Add the wet ingredients to the bowl of dry ingredients and fold in just until combined. Fold in the walnuts and blueberries.

Scoop ¼ cup of batter for each cookie onto the baking sheet. Bake 20 to 24 minutes, or until browned around the edges. Cool on the pan for 5 to 10 minutes and then transfer to a wire rack to finish cooling. If you take them off the sheet too soon, the cookies may fall apart.

When cookies are completely cool, they can be stored in an airtight container or frozen.