Heat 2 tbsp of the olive oil in a large heavy pan, then add the onions and fry for about 10 minutes until lightly browned and soft. Transfer to a plate.
Toss the chicken in the seasoned flour. Heat the remaining 1 tbsp of oil in the pan, then add the chicken and fry until evenly browned.
Add the chicken broth, onions and their juices, orange juice and zest, sherry and Worcestershire sauce. Bring to the boil, then reduce the heat, cover and simmer for 25 minutes until the chicken is tender.
Stir in the mushrooms and cook for 5 minutes. Taste and season with salt and black pepper if necessary. Just before serving, sprinkle over the chopped parsley and serve with boiled rice.