Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a medium bowl, whisk together the flour, rolled oats, baking soda, baking powder, cinnamon, nutmeg, and salt. Set aside.
In a large bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy.
Add the pumpkin puree, egg, and vanilla extract to the butter mixture, mixing until well combined.
Gradually add the dry ingredients to the wet mixture, stirring until just combined.
Gently fold in the mini marshmallows, chocolate chips, and graham cracker crumbs.
Using a tablespoon or cookie scoop, drop rounded balls of dough onto the prepared baking sheet, spacing them about 2 inches apart.
Bake in the preheated oven for 10-12 minutes or until the edges are golden brown and the tops look set.
Remove from the oven and allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.
Notes
Stack the cookies on a decorative plate, and drizzle melted chocolate over the top for an indulgent finishing touch. Optionally, sprinkle some extra graham cracker crumbs on top for added texture.