In a Dutch oven, heat 2 tablespoons of oil over medium heat. Add chicken and sweet potatoes. Season with salt and pepper and cook until chicken is no longer pink, about 4-6 minutes. Remove from pan and set aside.
Add remaining oil and onion to Dutch oven. Saute until onions become translucent, about 3-4 minutes.
Stir in Dei Fratelli Diced Tomatoes, cooked chicken, sweet potatoes, broth, peanut butter, thyme, and cayenne. Reduce heat and bring to a simmer for 20 minutes, or until sweet potatoes are tender.