Prep the coating: In a microwave-safe bowl or over a double boiler, melt white chocolate chips with coconut butter/oil until smooth.
Mix in matcha: Sift the matcha into the melted chocolate and stir until vibrant green and fully combined then add a pinch of salt.
Coat the cereal: Place cereal in a large bowl. Pour the matcha-chocolate mixture over the cereal and gently toss until every piece is coated.
Powder finish: Transfer coated cereal into a large zip-top bag or lidded container. Add powdered sugar then shake until fully coated.
Cool + serve: Spread puppy chow on a baking sheet lined with parchment to cool and set. Add optional mix-ins (freeze-dried berries, coconut, etc.) before serving.