Pre-heat your slow cooker. See your manufactures recommendations.
Add the chicken, onion, carrot, peppers and leek to the pot.
Put the cornflour in a bowl and gradually whisk in the pineapple juice to make a paste. Whisk in the tomato puree, Chinese 5 spice, vinegar, and soy sauce.
Add the pineapple mixture to the pot with the passata, garlic, ginger and the stockpot.
Replace the lid and cook for 5-6 hours on high, or 7-8 hours on low.
30 minutes before the end of cooking, add the bamboo shoots and pineapple * (and give it a good stir).
Discard the star anise, divide and serve.