1. Preheat oven to 350 degrees. Place foil in a 9x13 pan and spray with cooking spray.
2. Mix the 1st 4 ingredients until blended; the mixture will be thick. Press half the mixture into the pan.
3. Bake for 10 minutes. Sprinkle with half the chocolate and half the nuts. Top with peanut butter. Top with the rest of the cake mix, chocolate, and then nuts. Press down gently .
4. Bake for 15 minutes, cool for 1 hour. Put in the refrigerator for at least 4 hours before cutting.