Place chicken and water in a stock pot and add onion, celery and garlic. Cover and bring to the boil. Reduce heat and simmer until chicken is tender, about 45 minutes.
Remove chicken from stock and set aside to cool. Skim off fat. Smash cooked garlic cloves against side of pot. Add undrained tomatoes, carrots, cumin, cayenne pepper, white pepper and stock cube to the stock. Cover and simmer 30 minutes.
Add sweetcorn, spring onions and coriander. Simmer 10 minutes longer.
Skin and bone chicken, then dice or shred into bite-size pieces. Add chicken to soup along with cooked rice. Heat through. Season with salt to taste. Ladle into bowls and garnish with cheese and tortilla chips.