Add the peanut butter, chocolate, and coconut oil to a microwave safe bowl. Microwave in 30 second intervals, stirring each time, until melted. Stir in the protein powder.
Pour the peanut butter mixture over the rice chex and toss to combine and coat the chex.
Working in batches if needed, add the chex to a plastic bag and sprinkle with the powdered sugar. Toss and shake until the chex is well coated with the powdered sugar.