01 - Preheat oven to 350°F (175°C). Line an 8x8-inch baking pan with parchment paper.
02 - Mash bananas in a large mixing bowl until smooth. Incorporate peanut butter, honey or maple syrup, and vanilla extract. Mix until homogeneous.
03 - In a separate bowl, whisk oats, protein powder, ground flaxseed, cinnamon, and salt.
04 - Add dry ingredients to wet mixture. Stir until fully incorporated. Gently fold in chocolate chips or chopped nuts, if using.
05 - Spread batter evenly in prepared pan and smooth the surface with a spatula.
06 - Bake for 20 to 25 minutes, until edges are golden and center is set.
07 - Let bars cool completely in pan. Slice into 12 bars once cooled.