Preheat your oven to 350°F (175°C). This step ensures that your bars bake evenly and come out perfectly.
Line an 8x8-inch baking dish with parchment paper, allowing some overhang on the sides. This will help you lift the bars out easily once they are baked.
In a large mixing bowl, combine the mashed banana, peanut butter, and coconut milk. Use a spatula to mix until smooth and well combined.
To the wet mixture, add the rolled oats, almond flour, cocoa powder, ground flaxseed, and protein powder (if using). Stir until everything is evenly mixed. The batter should be thick and cookie-like.
Gently fold in the chopped peanuts, ensuring they are evenly distributed throughout the mixture.
Transfer the mixture to the prepared baking dish. Use the spatula to spread it evenly, pressing down slightly to pack it in.
Place the baking dish in the preheated oven and bake for 25-30 minutes, or until the edges are golden brown and the center is set.
Once baked, remove the dish from the oven and let it cool in the pan for about 10 minutes. Then, use the parchment overhang to lift the bars out of the dish and transfer them to a wire rack to cool completely. Once cooled, slice into bars and enjoy!