To make the sauce, place the pineapple in a high-powered blender or food processor and blend to a juice. Pour into a small bowl. Add the tamari or soy sauce, honey, vinegar and chilli flakes (if using) and whisk until well combined.
Place the rice and 200 ml of water in a small saucepan over high heat and bring to the boil, stirring occasionally. Cover and reduce the heat to medium–low. Simmer for 20–25 minutes or until the liquid is absorbed and the rice is tender. Remove from the heat and leave to stand, covered, for 5 minutes.
Meanwhile, heat the oil in a large non-stick frying pan over medium–high heat. Add the onion and carrot and cook for 2–3 minutes, stirring occasionally.
Add the garlic, ginger and chicken and cook for 5–7 minutes or until the chicken is cooked through, stirring frequently.
Reduce the heat to medium and add the green and red peppers and courgette. Cook for 4–5 minutes or until tender-crisp. Add the pineapple and cook for a further 2 minutes.
Add the sauce mixture to the chicken and vegetables and bring to the boil, stirring occasionally.
Whisk the milk and cornflour together in a small bowl, then gradually stir into the chicken and vegetable mixture. Cook for 2–3 minutes or until the sauce has thickened, stirring constantly.
To serve, place the rice in two serving bowls and top with the sweet and sour chicken. Sprinkle over the coriander and chilli.