Gather all ingredients. Preheat the oven to 350 degrees F (175 degrees C). Line 2 baking sheets with parchment paper.
Place 1 ¾ cups of the oats in a blender or food processor. Blend or process to a fine powder.
Beat butter with an electric mixer in a bowl for 30 seconds. Beat in peanut butter and maple syrup until smooth. Beat in egg and vanilla just until combined.
Combine oat flour, baking soda, salt, and cinnamon in a small bowl. Add oat flour mixture to peanut butter mixture and beat in until combined.
Fold in remaining 1 cup oats, blueberries, and walnuts.
Drop generous ¼ cup portions of the dough onto the prepared baking sheets, about 6 cookies per sheet, and lightly flatten. Bake until browned, about 18 minutes.
Let cool on baking sheets for 5 minutes. Transfer to wire racks to cool completely.
