Preheat the slow cooker if necessary; see the manufacturer's instructions. Heat the oil in a frying pan, add the chicken thighs and fry, stirring, until browned on all sides. Mix in the white sliced spring onions, carrots and ginger and cook for 2 minutes.
Stir in the pineapple chunks and their juice and the stock. Put the cornflour, tomato purée and sugar into a small bowl, then gradually mix in the soy sauce and vinegar to make a smooth paste. Stir into the frying pan and bring to the boil, stirring.
Tip the chicken and sauce into the slow cooker pot, add the bamboo shoots and press the chicken beneath the surface of the sauce. Cover with the lid and cook on low for 6–8 hours.
When almost ready to serve, add the green spring onion, the beansprouts and mangetout to the slow cooker pot and mix well. Replace the lid and cook, still on low, for 15 minutes or until the vegetables are just tender. Spoon into rice-filled bowls.