1. Preheat oven to 350 degrees Fahrenheit (180 degrees Celsius).
2. Roast pecans or walnuts for five to six minutes until golden. Roast the peanuts for four to five minutes. Set aside.
3. Melt the chocolate with oil in a microwave or double boiler. Transfer to a bowl. Add the remaining brownie ingredients, including the roasted pecans or walnuts, and mix until combined. Transfer half the mixture to a disposable eight-by-12-inch (20×30-centimeter) pan.
4. Heat the caramel and peanut butter in the microwave and mix well until combined. Swirl this mixture through the remaining half of the brownie batter. Fold in the roasted peanuts. Carefully pour over the brownie batter in the pan.
5. Bake at 350 degrees Fahrenheit (180 degrees Celsius) for half an hour, or until a toothpick comes out clean.