Preheat the oven to 350 °F (175 °C). Line two muffin pans with 20 paper liners.
In a medium bowl, mix together the flour, baking powder, baking soda, salt, cinnamon, ginger, and nutmeg.
In a larger bowl, whisk the eggs, pumpkin puree, sugar, and oil.
Add the dry mix to the wet and stir just until combined. Do not over mix!
Divide the batter among the liners, filling each one almost full, and bake for about 20 – 24 minutes, or until a toothpick inserted in the center comes out clean. Let cool for 3 minutes in the pan and then remove to a wire rack to cool completely, about 1 hour.
Once the cupcakes have cooled, prepare the frosting. Beat the butter and cream cheese until soft and smooth. Add the salt and vanilla and beat until combined. Add in the powdered sugar, 1/2 cup at a time, and beat until fluffy.
Spread about 1 ½ tablespoons of frosting over each cooled cupcake.
Twist the Oreos apart and place the side without frosting face up on the cupcake. You can also use whole Oreos if you prefer.
Melt the chocolate in a small saucepan over low heat, stirring constantly until melted. Pour into a piping bag.
Pipe 4 legs on both sides of the Oreo. Pipe a tiny bit of chocolate on the bottom of two eyes and place on the Oreo.
Keep decorated cupcakes refrigerated for one day until ready to serve. Keep undecorated cupcakes at room temperature for up to 3 days. The Oreos get slightly soft over time so decorate just a few hours before serving, if possible.