Heat the oil in a large saucepan over medium-low heat. Cook onion, garlic, ginger and rosemary for 5 minutes or until soft.
Add chicken, celery and chilies. Cover with water. Increase heat to high. Bring to the boil. Reduce heat to low. Cover. Simmer for 1 hour, skimming the surface occasionally. Cool. Chill for 2 hours or overnight.
Remove and discard fat from surface of stock. Transfer chicken to a chopping board. Discard skin and bones. Shred chicken.
Bring the stock to the boil over high heat. Reduce heat to medium. Stir in sweet potato. Cook for 10 minutes or until tender. Stir in peas and chicken for 2-3 minutes or until heated through. Stir in soy sauce. Season with pepper.