Pre-heat oven to 350°. Spray the inside of 3 half quart (about 8 fl oz capacity) baking dishes with non-stick cooking spray. Set aside.
In a medium bowl, whisk together oat flour, protein powder, baking powder, cocoa powder, and salt until well combined. Set aside.
In another bowl, whisk together milk, eggs, maple syrup, and vanilla extract. Pour into bowl with dry ingredients and mix until completely incorporated and not dry flour remains visible. The batter should be thick and sticky. Fold in chocolate chunks.
Add the batter to the prepared baking dish and spread out with a spatula to make an even layer that reaches the edges.
Bake for 18-20 minutes. They should puff up and begin to brown lightly on top, and touching it should not leave a mark. Set aside on a cooling rack.
Top slightly cooled oats with a dollop of marshmallow creme and crushed graham crackers (if desired) before serving.