Grease a 9 x 5-inch loaf pan and line it with parchment paper. Set aside.
Place peanut butter, chocolate chips, coconut oil and maple syrup in a microwave-safe bowl.
Microwave on high in 15-second increments until the mixture is glossy and melted. Stir after each 15-second period in the microwave. If you overdo it and the mixture turns solid, add another tablespoon of coconut oil and stir. It should turn liquid and glossy again.
Using a rubber spatula or a spoon mix in protein powder and rice crispy cereal. Keep mixing until fully incorporated and there is no specks of powder visible.
Transfer the mixture into the prepared loaf pan. Use a jar with a flat bottom or a measuring cup to press down to create an even layer.
Top with crushed peanuts (if you want) and press down again.
Cover with plastic wrap and refrigerate for at least 2 hours.
Carefully remove the paper from the loaf pan, transfer to a cutting board and cut into 5 long bars, then cut lenthwise to create 10 square-ish pieces.
Store the bars in an airtight container in the fridge for up to 4 days.