In a large mixing bowl, combine the rolled oats, peanut butter, honey (or maple syrup), protein powder, cocoa powder, and salt. Stir until well combined and a thick mixture forms.
If desired, fold in the dark chocolate chips and chopped nuts for added texture and flavor.
Line an 8x8-inch baking dish with parchment paper, leaving some overhang for easy removal.
Transfer the mixture to the prepared baking dish and press it down evenly using a spatula or your hands. Make sure it’s packed tightly.
Refrigerate the bars for at least 1 hour to firm up.
Once chilled, lift the bars out of the dish using the parchment paper and cut them into squares or rectangles.
Store the bars in an airtight container in the refrigerator for up to one week.