In a medium-sized bowl, whisk together the flour, baking soda, salt, and pumpkin pie spice. Set aside.

Using a stand mixer with the paddle attachment, or a hand mixer, cream the butter and brown sugar until smooth, about 1-2 minutes. Add the eggs and vanilla extract, continuing to mix until well combined.

Slowly incorporate the dry ingredients into the wet mixture, ensuring everything is blended evenly without overmixing. Add the oats and mix until fully combined.

Scoop out the dough using 2 tablespoons for each cookie, placing them on a parchment-lined cookie sheet. Cover the dough with plastic wrap and refrigerate for at least 1 hour.

Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper or a silicone baking mat. Arrange the chilled dough balls 2 inches apart on the prepared sheets.

Bake the cookies for 10-12 minutes, or until the bottoms are slightly golden. Allow the cookies to cool on the sheets for 10 minutes before transferring them to a wire rack to cool completely.

Store the cooled cookies in an airtight container for up to 4 days, or freeze them in an airtight container or resealable bag for up to 2 months.