Preheat oven to 160c / 325 degrees F.
In a large mixing bowl, mash your bananas until smooth. It is ok to have a few small chunks left. Stir in the peanut butter and maple syrup. Mix well.
Then, add in oats and protein powder into the bowl. Mix until everything is well incorporated.
Transfer the mixture to a lined or greased baking pan. Using the back of a spoon or spatula, gently press down the granola mixture so that a thin, even layer is formed. Do make sure that the mixture is evenly spread out, or else the thin part will be burnt, while the thicker part undercooked !
Bake it for 20 minutes, then rotate the pan and bake them for another 10-20 minutes, or until golden brown. It might not be crunchy yet, but don't worry as it will continue to cook and crisp up in the pan after pulling out from the oven.
Let the protein granola cool down to room temperature, for about 1 hour. Then, using a spoon or your hands, break them up into chunks.
It is now ready to be enjoyed !