Preheat the oven to 375 degrees Fahrenheit.
Add 1 cup boiling water, 1/4 cup cocoa powder, 1 1/4 teaspoons pure liquid monk fruit sweetener, 1 teaspoon vanilla extract, and 1/4 teaspoon salt to a large mixing bowl. Mix well until the cocoa powder is dissolved.
Add 1 cup creamy natural peanut butter, then mix well.
Add 1 cup unsweetened protein powder, then when the mixture is cool enough to handle, use your hands to combine the ingredients until a thick dough is formed (I recommend wearing kitchen gloves to make this easy). If the dough is too crumbly, add 1/4 cup of cold water, plus additional water if necessary, 1 tablespoon at a time, until the dough is moist enough to hold its shape. Some types of protein powder are more absorbent than others, which affects how much water is needed.
Divide the dough evenly into 10 portions, then use your hands to shape into bars and place them on a sheet pan lined with parchment paper.
Bake for 12 minutes.
Let cool completely before removing from the pan and serving.
Optional step: drizzle melted low-carb or keto-friendly dark chocolate on top of the cooled bars, then place them in the fridge for 45 minutes or until the chocolate has hardened before serving.