Put oil and popcorn kernels in a large pot over medium-high. When the first kernel pops, cover the pot and remove it from the heat for about 30 seconds.
Place pot back on the stove and once kernels start popping, vigorously shake the pot back and forth, keeping it on heat. Once popping slows, take pot off the heat and remove cover. Put popped popcorn in a large bowl.
Add graham cracker crumbs and marshmallows and toss to combine.
Put chocolate chips or roughly chopped chocolate in a heat-safe bowl and microwave at 50% power for 30 seconds. Remove bowl and stir gently. Put back in the microwave and continue heating for 30 second intervals, stirring after each, until the chocolate is completely melted.
Drizzle the melted chocolate over the popcorn mixture and gently stir the mixture to coat in chocolate.
Pour popcorn mixture onto a baking sheet to allow chocolate to set.