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 oat flour, protein powder, baking powder, and fine sea salt.
In a separate bowl, stir together the almond butter, maple syrup, and vanilla extract until smooth.
Combine the wet and dry ingredients, adding almond milk one tablespoon at a time until a stiff dough forms.
Press the mixture firmly and evenly into the prepared baking pan using a spatula or the bottom of a measuring cup.
Bake for 15 to 18 minutes until the edges are golden brown and the center is firm to the touch.
Remove from the oven and immediately sprinkle the flaky sea salt over the surface.
Allow the bars to cool completely in the pan for at least 30 minutes before slicing into 12 rectangular bars.