Heat oil in a Dutch oven over medium-high heat. Add onion; cook 5 minutes or until almost tender. Combine cumin, coriander, and cinnamon in a small bowl; sprinkle over onion in pan. Cook 1 minute. Add chiles and garlic to pan; cook 2 minutes or until chiles soften. Add broth and next 4 ingredients (through rind) to pan; bring to a boil. Add chicken to pan; cover, reduce heat, and simmer 10 minutes or until chicken is done. Remove chicken from pan; shred with 2 forks. Set aside.
Add chocolate to chile mixture; let stand until chocolate melts. Using an immersion blender in pan, puree the chocolate mixture until smooth. Cook over medium heat 20 minutes or until reduced to 3 1/2 cups. Add shredded chicken to sauce; stir in salt and pepper.