Start by placing your 12 Oreos in a large Ziploc bag. Using a rolling pin or a heavy object, crush the Oreos until they reach a fine crumb consistency.
In a mixing bowl, combine the crushed Oreos and melted butter. Stir until the crumbs are evenly coated and start to clump together.
In a microwave-safe bowl, melt the white chocolate chips in 30-second intervals, stirring in between until smooth.
Pour the melted white chocolate over the Oreo and butter mixture. Stir until well combined. Then, gently fold in the Chex Mix and M&Ms until evenly distributed.
Line a baking sheet with parchment paper. Pour the Oreo crust mix onto the sheet and spread it out evenly.
Place the baking sheet in the refrigerator for about 30 minutes to allow the mix to set.
Once set, break the mix into pieces and serve! Enjoy it as a standalone snack, or use it as a topping for ice cream or yogurt.