Prepare Your Baking Pan: Grease a 9x13-inch baking pan with a little coconut oil to prevent sticking.
Melt Marshmallows and Coconut Oil: In a microwave-safe bowl, combine the marshmallows and coconut oil. Heat in 30-second intervals, stirring until smooth.
Mix in Protein Powder: Stir in the protein powder until well combined.
Add the Cereal: Gently fold in the crispy brown rice cereal until evenly coated.
Press into the Baking Pan: Transfer the mixture into the prepared baking pan and press down firmly.
Cool and Cut: Allow to cool completely at room temperature and then cut into squares.