Heat the oil in a large frying pan over a medium heat, then add the onions and courgettes. Cook for 5-10 minutes, until lightly golden.
Add the chicken pieces to the pan and fry for a further 5 minutes. Pour in the sauce and bring to a simmer. Cook for a further 8 minutes.
Meanwhile, cook the rice following pack instructions, then drain and serve with the sweet and sour chicken.