Line a baking sheet with wax paper, parchment paper, or a silicone baking mat.
Melt the milk chocolate chips in a microwave-safe bowl, stirring every 30 seconds until smooth, then spread evenly on the prepared baking sheet.
Melt the white chocolate chips in another bowl, stirring every 30 seconds until smooth, then fold in the vegan marshmallows fluff.
Dollop spoonfuls of the white chocolate mixture over the milk chocolate layer and create a marbled effect using a butter knife.
Sprinkle the Golden Grahams cereal and vegan marshmallows bits over the top, pressing them down gently.
Chill in the freezer for about 30 minutes or in the refrigerator for an hour until firm.
Break the bark into pieces and enjoy!