Heat 1 Tbsp olive oil in heavy stock pot over medium-high heat. Season chicken with salt & pepper. Sauté in batches until golden brown, about 3 minutes per side. Place in large bowl until all remaining chicken is browned. Place chicken back in pot with any juices. Add broth, balsamic, and orange juice. Bring to gentle simmer and cook for 25 minutes until chicken is tender.
In a separate pot heat 2 Tbsp olive oil over medium-high heat. Add onions and sauté until golden brown, about 18 minutes. Reduce heat to medium. Add pumpkin seeds, garlic, cumin, and coriander. Sauté until seeds and garlic begin to colour, about 2 minutes. Add chillies and stir until soft, approximately 3 minutes.
Transfer cooked chicken to large bowl and reserve. Pour chicken cooking liquid into saucepan with onion mixture. Add orange peel, oregano, and cinnamon to pan. Cover and simmer until chiles are very soft, stirring occasionally, about 30 minutes.
Remove from heat and working in small batches, transfer sauce mixture to blender and purée until smooth. Return to reserved pot. Season sauce to taste with salt and pepper. Coarsely shred chicken and return to sauce; stir to coat.
Can be made up to two days ahead of time. Delicious the next day when it's had time to marinate! Simply chill in covered container and rewarm over low heat before serving. Serve with rice or warm corn tortillas along with a garnish of chopped fresh cilantro.
Serves 6