Preheat the oven to 450°F.
Place the tots on a rimmed baking sheet and drizzle them with the oil. Toss the tots gently to coat them evenly with the oil, then spread them out in an even layer.
Bake the tots, flipping them with a spatula halfway through cooking, until evenly browned and crispy, about 25 minutes.
Meanwhile, place the graham crackers and sugar in the bowl of a food processor and process until smooth.
When the tots come out of the oven, immediately put them in a large bowl and pour the graham cracker mixture on top. Toss to coat.
Pile the coated tots into a 12-inch cast iron skillet or onto the center of a parchment-lined rimmed baking sheet, reserving any bits of graham cracker mixture that remain in the bowl. Top the tots with the chocolate and marshmallows, then sprinkle the reserved graham cracker mixture on top.
Bake until the marshmallows brown on top and the chocolate melts, about 10 minutes.
Serve immediately, using forks (or you're fingers if you're brave) to eat the tots right out of the pan.