Heat oven to 350°F (180°C) and fold a 7 x 7 inch (15 x15 cm) brownie pan with parchment paper.
In a large bowl mash the bananas and combine with Greek yogurt, vanilla extract, cinnamon and a pinch of salt. For sweetener oats, add 2 to 4 tablespoons of maple syrup or honey to taste. Stir until smooth.
Add rolled oats and protein powder (or oat flour) to the wet mixture, then stir until combined. You can optionally add extra mix-ins like chopped walnuts or raisins.
Transfer the dough to the prepared baking pan and spread it out evenly.
Bake in hot oven for 15 to 20 minutes, or until the protein oats have set in the center. Let cool to temperature before slicing and topping with vanilla glaze.