In a large saucepan, combine chicken, water, celery, bay leaf, onion and garlic. Season with salt and pepper. Cook until chicken is tender. Strain, reserving the stock. Remove skin and bones from the chicken; set the meat aside.
Toast the sesame seeds lightly in a frying pan, stirring constantly, until they are fragrant. In a food processor or blender, purée the sesame seeds and almonds with 225ml (8 fl oz) of the reserved chicken stock.
Heat oil in a frying pan over medium low heat. Add the sesame seed and almond mixture, and cook for 5 to 8 minutes, or until thickened. Stir in another 225ml reserved chicken stock and bring to the boil. Add chicken stock cube and reduce heat to simmer for 5 minutes. Stir in the chopped chillies, olives, capers and chicken. Simmer for 10 minutes, and serve hot.
Guero chillies are small and yellow, giving medium heat. They also go by the simpler term "yellow hot chilli". If you're unable to find this variety, use a Hungarian wax chilli or poblano.