Line baking sheets with parchment paper; set aside.
In large bowl, beat butter with sugar until fluffy; beat in egg and vanilla. In separate bowl, whisk together rolled oats, flour, baking powder, baking soda and salt - stir into butter mixture until combined. Stir in chocolate chips.
Drop by heaping 1 tbsp, about 2 inches apart, onto prepared pans. Bake in top and bottom thirds of 375°F oven, rotating and switching pans halfway through, until golden, about 12 - 15 minutes. Transfer to rack; let cool.