Microwave chocolate in large microwavable bowl on HIGH 1-1/2 minutes; stir. Microwave an additional 30 seconds. Stir until chocolate is completely melted.
Stir in 3/4 cup each of the graham snacks and marshmallows.
Spread onto wax paper-covered baking sheet. Top with remaining 1/4 cup each graham snacks and marshmallows.
Refrigerate 1 hour or until firm. Break into pieces.