Preheat oven to 350°F. Line 20 muffin cups with paper liners; set aside. In a medium bowl, whisk together flour, sugar, cinnamon, baking soda, salt, and espresso powder. In another bowl, whisk together oil, pumpkin, and eggs until smooth. Whisk in dry ingredients until just combined.
Divide batter between muffin cups. Bake until a toothpick inserted into the center of cupcake comes out clean, 20 to 24 minutes. Let cool 10 minutes, then transfer cupcakes to a wire rack to cool completely.
In the bowl of a stand mixer, beat butter on medium speed until light and fluffy, about 2 minutes. Slowly add confectioners' sugar and mix until smooth. Add espresso, vanilla, and salt; mix until well combined. Spread a generous amount of frosting over each cupcake.