1. Heat oil in a Dutch oven over medium-high heat. Sprinkle chicken with 1/2 teaspoon salt and 1/4 teaspoon pepper. Add chicken, flesh side down. Cook 10 minutes; turn thighs after 5 minutes. Cool; shred. Discard bones.
2. Add onion, leeks, and ginger to pan; sauté 10 minutes. Add garlic; sauté 1 minute. Place parsley sprigs and bay leaves on cheesecloth. Gather edges; tie securely. Add sachet to pan.
3. Combine peanut butter, 1/4 cup water, and tomatoes, stirring well. Add peanut butter mixture, chicken stock, 2 cups water, sweet potato, and ground red pepper to pan; bring to a boil. Return chicken to pan. Reduce heat to medium, and simmer 20 minutes, stirring occasionally. Remove from heat; discard sachet.
4. Ladle about 1 1/3 cups soup into each of 6 bowls, and top each serving with 2 teaspoons chopped fresh flat-leaf parsley and 1 teaspoon chopped unsalted peanuts.