Preheat the oven to 350°F (175°C). Line a large baking sheet with parchment paper.

In a small bowl, combine the ground flaxseed and warm water. Let sit for 5 minutes until thickened.

In a large mixing bowl, combine the oat flour, rolled oats, almond flour, lemon zest, baking powder, baking soda, cinnamon, and salt.

In a separate bowl, whisk together the almond butter, melted coconut oil, and maple syrup until smooth.

Stir the flaxseed mixture into the wet ingredients.

Add the wet ingredients to the dry ingredients and gently fold until combined.

Fold in the walnuts and blueberries.

Scoop about ¼ cup of batter for each cookie onto the prepared baking sheet.

Bake the oatmeal breakfast cookies for 20–24 minutes, or until lightly golden around the edges.

Allow the cookies to cool on the baking sheet for 10 minutes before transferring them to a wire rack.

Cool completely before storing.