Preheat the oven to 350°F and line cupcake pans with 18 paper liners.
Place the oats in a food processor or blender and pulse a few times. You don't want to turn them completely into flour. The goal is simply to break them into smaller pieces so you get the oatmeal flavor without large, chewy oats throughout the cake.
In a medium bowl, whisk together the flour, oats, baking powder, baking soda, salt, cinnamon, nutmeg and ginger. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, beat the softened butter, brown sugar and granulated sugar together for about 2–3 minutes, until light and fluffy.
Add the eggs one at a time, mixing well after each addition. Mix in the vanilla.
Add about one-third of the dry ingredients, followed by half of the buttermilk. Continue alternating the dry ingredients and buttermilk, beginning and ending with the dry ingredients. Mix just until everything is combined. Be careful not to overmix the batter.
Divide the batter evenly between the cupcake liners, filling each about 2/3 full.
Bake for 18–21 minutes, or until the tops spring back lightly when touched and a toothpick inserted into the center comes out clean or with a few moist crumbs.
Allow the cupcakes to cool in the pan for about 5 minutes before transferring them to a wire rack to cool completely.