1. In a large mixing bowl, cream together butter, peanut butter and brown sugar. Mix on medium speed for one minute.
2. Add eggs and mix for one more minute.
3. In a separate bowl, combine flour, baking powder, salt.
4. Add flour mixture to butter/sugar/egg mixture. Mix on medium speed for 1 minute.
5. Gradually, stir in rolled oats, followed by the nuts then chocolate chips.
6. Pour into a greased 9x13 inch baking pan.
7. Bake at 350F oven for 20 minutes. Reduce heat to 325F (edges will be browning) and bake for another 10-15 minutes.
8. Remove from oven and cool on wire rack for 15 minutes before cutting into squares.