In a small mixing bowl, combine the butter, sugars, and egg.
In a large mixing bowl, combine baking powder, baking soda, flour, and oats.
Combine the wet ingredients with the dry and stir until just incorporated.
Fold in chocolate chips.
Chill dough for 1 to 2 hours to minimize spreading.
Use a cookie scoop (1 1/2 Tablespoon-sized) to drop bits of dough onto a lightly greased baking sheet.
Bake for 10 to 12 minutes until the edges have slightly browned. Let cookies finish baking on the pan before serving.
Notes
It's easy to overbake these cookies. They won't look done in the middle when you first pull them out, but let them finish baking on the pan and they'll be perfect.