Preheat oven to 350°F (175°C) and line an 8x8 inch baking pan with parchment paper.
In a large mixing bowl, whisk together the rolled oats, protein powder, baking soda, and salt.
In a separate medium bowl, whisk together the applesauce, honey, egg, lemon zest, lemon juice, and vanilla extract until emulsified.
Combine the wet ingredients with the dry ingredients, stirring until a thick, uniform batter forms.
Gently fold in the fresh blueberries using a rubber spatula to prevent bursting.
Transfer the mixture to the prepared baking pan and press down firmly to create an even layer.
Bake for 22 to 25 minutes, or until the edges are golden brown and the center is firm to the touch.
Allow the bars to cool completely in the pan on a wire rack for at least 30 minutes before slicing into 12 equal portions.