In 4-quart Dutch oven, heat oil over medium-high heat. Add chicken and cook 5-6 minutes, stirring frequently, until browned. Add onion, bell pepper, garlic and jalapeño chiles; cook 2 minutes, stirring frequently.
Stir in tomatoes, water, cocoa, chili powder, salt and cinnamon. Heat to boiling. Reduce heat to low; simmer uncovered 15-20 minutes or until chicken is no longer pink in center and chili is desired consistency.
Sprinkle individual servings with pepitas. Serve with corn tortillas.