Preheat oven to 350 degrees.
Combine the cake mix, eggs and oil until well blended.
Drop 1 TBSP dough balls onto baking sheet lined with parchment paper.
Slightly flatten each dough ball.
Bake for no more than 7 minutes. If your oven runs hot, reduce heat to 325deg and check at 6 min.
Remove baking sheet from oven and add half a marshmallow and chocolate square on each cookie and carefully press down with graham cracker.
Return to over for 1 minute and 30 seconds, then remove from oven.
Chocolate and marshmallow will be melted. Slightly push the graham crackers down, if needed.
Cool on wire rack.
If the chocolate hasn't hardened enough, pop in the fridge for about 10 minutes.
Store in sealed container.