In a stand mixer, cream together butter and sugars. Add egg and vanilla, mixing until combined. Add cinnamon, nutmeg, salt, baking powder, flour and oatmeal. Mix, increasing speed until ingredients are fulling incorporated. Add in chocolate chips.
Using a cookie scoop, scoop out balls of dough and shape into even balls. Place on prepared baking sheet 2 to 3-inches apart. Flatten cookies to 3/4-inch using the palm of your hand.
Bake for 12-15 minutes or desired crispness. Allow cookies to rest on pan for 5-10 minutes prior to transferring to a wire rack to cool completely.
Store cookies in an airtight container.
For larger cookies, use an ice cream scoop and bake for 20-25 minutes.