Beat together the sugars and butter until combined, then add eggs and vanilla, and beat until fluffy.
Mix in the flour, powder, soda, salt, and cinnamon until combined. Stir in oatmeal and chocolate chips until combined, the batter will be very stiff.
Chill dough for 30 minutes before baking.
Preheat oven to 375 degrees. Measure about 1 1/2 tablespoons of dough (I use a medium cookie scoop) and roll into a ball and place on a cookie sheet lined with parchment paper or a baking liner.
Bake for 9 minutes, they will not look completely done but will be slightly brown around the edges. Move to a wire rack and cool completely.
Notes
For the chocolate chips in this recipe you can use any mix you want. Stick with semi-sweet for a classic flavor, or go with a combo of semi-sweet/milk/dark/white/butterscotch.