Preheat oven to 375 degrees F.
Line two large baking sheets with parchment paper. Set aside.
In a small bowl, combine the flour, baking soda, baking powder, salt and cinnamon. Set aside.
Place softened butter, granulated sugar and brown sugar in the bowl of a standing mixer and beat until combined.
Add egg and vanilla and beat on medium speed until the mixture is light (about 30-60 seconds).
Add dry ingredient mixture and beat on low speed until just combined.
Add oatmeal and beat on low speed until combined.
Add mix ins (if desired) and stir until evenly distributed in the dough.
Use a 1 ½ to 2 TBS cookie scoop to measure out the dough.
Roll the dough into a ball and place on the prepared cookie sheet. Repeat until all the dough is used.
Gently and very slightly press down tops of cookies until they are flat.
Bake in preheated oven for 8-10 minutes until the top is just set.
Let sit on the baking pan for 5 minutes before transferring to a wire rack to cool.