Split the doughnuts across the middle. Place the lids on a wire rack with a tray underneath. Mix the melted chocolate with the vegetable oil. Spoon melted chocolate onto each doughnut lid, then sprinkle the crushed graham crackers on top. Leave in the fridge for 30 minutes or until firm.
When the chocolate has set, arrange 5 small marshmallows on each of the bottom halves of doughnuts. Use a blowtorch to caramelize them, then top with the chocolate lids.