Line a 13" x 9" pan with aluminum foil or parchment paper. Set aside.
In a large mixing bowl, stir together flour, oats, baking powder and salt. Set aside.
In another large mixing bowl, beat butter and peanut butter with an electric mixer for 30 seconds. Add both sugars and beat until light and fluffy, about 3 minutes.
Add eggs, one at a time, beating well after each one.
Add the flour in two additions, mixing well after each.
Stir in chocolate.
Spread the dough into the prepared pan.
Bake 23 to 26 minutes, or until the center is set and edges slightly browned.