Grind the walnuts and dates in a food processor until finely ground. Add the tahini or almond butter and process until well mixed.
Add the cocoa powder and peanut butter powder and pulse to mix well. Transfer the brownie mixture to an 8-inch square baking pan. (If you line the pan with parchment paper, it will make it easier to remove the brownies.) Use your fingers to press the mixture evenly into the pan. (You can place a piece of parchment paper on top of the mixture as you press it into the pan to prevent it from sticking to your hands.)
Once the protein brownies are firmly pressed into the pan, sprinkle the top evenly with the crushed/whole pecans/walnuts, pressing them into the top of the brownies. Cover and refrigerate for at least 1 hour before cutting into squares
Store these brownies in the fridge for a firmer texture, or at room temp for meltier fudgier texture. They can last for up to a week and can be easily frozen.