For the chicken balls, place the chicken, scallions, Chinese five-spice powder, red chili and seasoning into a bowl and mix to completely combine. Mould the mince mixture into golf ball-sized balls, then dredge in cornflour.
Heat the vegetable oil in a deep-sided non-stick frying pan over a medium heat. Add the chicken balls and fry for 8-10 minutes, turning regularly, until golden-brown all over and completely cooked through. Remove from the pan and drain on kitchen paper.
For the sauce, place the cornflour, water, sugar, gluten free soy sauce, vinegar and tomato puree into a pan over a medium heat and mix well. Cook, stirring constantly, for 5-6 minutes, then add the peppers, pineapple chunks and scallion and stir well.
To serve, place a large spoonful of cooked white rice onto each plate and place 3-4 chicken balls on top. Pour the sauce over and serve.