Whisk together the flour, cinnamon, baking powder, baking soda, and salt. Stir in the oats. Set aside.
Using an electric mixer on medium speed, beat the butter and brown sugar until light and fluffy. Add the eggs, one at a time, mixing well after each addition. Mix in the vanilla.
Reduce mixer speed to low. Gradually add the flour mixture, mixing just until combined.
Refrigerate the dough for at least an hour.
Preheat oven to 350°F (175°C). Line baking sheets with parchment paper or silicone liners.
Drop the dough by 2-tablespoon portions (I use a #30 scoop) onto the prepared pans. Slightly flatten the top of each cookie. Sprinkle the top of each cookie with a pinch of coarse salt.
Bake, one pan at a time, 12 to 14 minutes, or until the edges of the cookies are browned.
Cool the cookies on the pan for 5 minutes. Then transfer the cookies to a wire rack to continue cooling.
