Whisk together flour, baking soda, pumpkin spice and salt in a bowl. Set aside.
Add butter and sugars to a mixing bowl and whip until creamy.
Whip in the vanilla extract, then whip in the egg.
Whip in the dry ingredients.
Whip in the oats and the coconut flakes.
Transfer the dough in the bowl to the fridge and chill for 10 minutes.
Divide the dough into two halves. Set each half onto a piece of parchment paper and shape (roughly) into a cylinder, about 2 inches in diameter.
For both batches, roll up the parchment paper, then twist the ends in opposite directions to form a tight log.
Transfer the logs into the fridge and chill for 1 hour.
Heat the oven to 375 degrees F.
Take the first log out of the fridge, remove the parchment paper and slice about 9 cookies out of it.
Transfer the cookies onto a baking sheet lined with parchment paper or a silicone baking mat. Leave at least 2 inches of space between each cookie.
Bake the cookies until they are lightly browned (about 14 minutes).
Let the cookies cool completely.
Repeat with the remaining log.*
For the drizzle:
Whisk powdered sugar and Bourbon together. Adjust with more powdered sugar or Bourbon to get the right consistency to drizzle the glaze.
Drizzle the glaze over the cookies and let dry.
Notes:
*If you have two baking sheets, use both to bake the cookies. If you only have one baking sheet, let it cool back down to room temperature before slicing and baking the second batch of cookies. Don't set the unbaked cookies on a hot baking sheet.