Preheat the oven to 350 and line two cookie sheets with parchment paper.
In a medium bowl, whisk the flour, oats, cinnamon, baking soda, ginger, nutmeg, and salt together until combined.
In the bowl of a stand mixer fitted with the paddle attachment, add the butter and two sugars. Beat them together on medium-high speed until it is light and fluffy (1-2 minutes).
Reduce the speed to medium and add the egg and vanilla, continuing to beat until creamy.
Add the dry ingredients and continue mixing on low speed until the flour is just combined. Then, fold in the carrots and pecans. The final dough will be a bit sticky.
Use a cookie dough scoop or a greased spoon to drop 1.5 tbsp at a time of the dough onto the lined cookie sheets. Make sure to spread them 2 inches apart. Bake for 12-14 minutes, or until the tops are set and edges start turning brown.
Remove the cookies from the oven and let them cool for 5 minutes on the cookie sheets before transferring to wire racks to cool completely.
Beat the butter and cream cheese together in a mixer on medium speed for 30 seconds or until they are combined and fluffy. Add the powdered sugar, vanilla, and cinnamon and continue beating until smooth and creamy.
Once the cookies have fully cooled, spread or pipe the bottom side of one with the cream cheese frosting. Find a similar sized cookie and place it on top to make a sandwich. Repeat with the other cookies. Enjoy!