Line a 9-inch brownie pan with parchment paper, length- and width-wise. In a stand mixer with the beater attachment, combine the applesauce, peanut butter, and stevia extract, mixing on low speed. Turn off the mixer and add the protein powder, cocoa powder, and salt, then mix again on low speed until fully combined. Add the oats and continue mixing until the mixture is evenly incorporated.

Transfer the mixture to the prepared pan, spreading it out evenly. Place a sheet of parchment paper on top and press the mixture down firmly until compact. Cover the pan and refrigerate overnight. The next day, slice and serve. To store, place the granola bars on a parchment-lined plate and keep them refrigerated for up to 1 week.