1-Preheat oven to 350ºF and line an: Preheat oven to 350ºF and line an 8×8″ baking dish with parchment paper.
2-Place bananas in a mixing bowl and: Place bananas in a mixing bowl and use a fork to throughly mash. Once pureed, stir in peanut butter, maple syrup, oil, and vanilla.
3-Add rolled oats, collagen or protein powder,: Add rolled oats, collagen or protein powder, chocolate chips, walnuts (if using), and salt; stir to combine.
4-Pour mixture into prepared baking dish: Pour mixture into prepared baking dish. If desired, sprinkle a few extra chocolate chips overtop. Transfer to the oven and bake for 28 to 32 minutes, until set. Remove from the oven and let cool in the pan for 30 minutes. Use the parchment paper to lift the bars out of the pan and let cool completely before slicing into.
5-Once cooled, slice into 12 bars: Once cooled, slice into 12 bars. (I also like sprinkling some flaky salt overtop, however totally optional.) Refrigerate after 2 days.