Preheat the oven to 400 degrees Fahrenheit. Line a large sheet pan with parchment paper. Set aside.
In a stand mixer fitted with the paddle attachment, beat together 1 cup packed light brown sugar, 1 cup granulated sugar, and 1 cup unsalted butter, at room temperature, until creamy 1-2 minutes. Add in 2 large eggs and ½ tablespoon vanilla extract and beat until combined.
In a separate bowl, combine 2½ cups quick oats, 1 teaspoon baking powder, 1 teaspoon baking soda, ½ teaspoon sea salt, 2 cups all-purpose flour, and 2 cups. milk chocolate chips. Whisk until combined. Add the oat mixture to the sugar and egg mixture and mix until just combined.
Roll out golf-ball sized dough balls and place 2 inches apart on the prepared baking sheet. Bake 6-8 minutes or until just lightly golden brown. Watch carefully to avoid over-baking; slightly under-baked oatmeal cookies make the best chewy cookies!