In a large mixing bowl, combine the rolled oats, protein powder, cocoa powder, and salt. Mix well.
In a separate bowl, mix together the peanut butter, honey (or maple syrup), and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients and stir until fully combined. If using, fold in the chocolate chips.
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 firmly into an even layer.
Refrigerate for at least 1 hour to set.
Once set, lift the bars out of the dish using the parchment paper and cut into squares or rectangles.