Preheat oven to 350°F and line large baking sheets with parchment paper.
In a medium bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon. Set aside.
In a large bowl, use a stand mixer to beat the butter, brown sugar, and granulated sugar on medium-high speed until smooth and well combined (about 1 to 2 minutes).
Beat in the eggs and vanilla, and then, on low speed, gradually add the flour mixture and beat until just combined.
Stir in the oats and chocolate chips.
Using a large spring-loaded cookie scoop, drop 3-tablespoon-sized balls of dough onto prepared cookie sheets and flatten slightly with the bottom of a measuring cup.
Bake for 14 to 15 minutes, or until the edges are slightly browned, rotating cookie sheets halfway through.
If you prefer a slightly softer cookie, bake for about 12-13 minutes, or until the edges are slightly brown but the middle still looks underdone (it will firm up while cooling).
Let the cookies cool on baking sheets for 5 minutes before removing to wire racks to cool completely.
