Preheat oven to 350 degrees F (175 degrees C). Line a baking sheet with parchment.
Spread oats out onto an unlined baking sheet in a thin layer, and toast until lightly browned, about 10 minutes; remove and allow to cool. Mix together the cooled oats, protein powder, whole wheat flour, and flax seed until thoroughly combined, and mix with peanut butter and honey. Mash the bananas into the mixture, and stir to combine. Press the dough down onto the parchment-lined baking sheet in a 1/2-inch layer.
Bake in the preheated oven until the edges of the dough are golden brown, about 15 minutes; cut into bars while warm, and allow the bars to cool. Wrap bars in plastic wrap, and refrigerate until ready to use.