Place rice in a microwave-safe container with the water. Cover with lid; microwave on high for 18 minutes or until tender.
Meanwhile, heat a teaspoon of oil in a wok over high heat; stir-fry buk choy with a splash of water for 1 minute or until wilted. Remove from wok. Add another teaspoon of oil to wok, stir-fry 1/4 of the chicken until cooked. Remove from wok and repeat until all chicken is cooked.
Stir cornflour and vinegar in small bowl; add to the wok. Cook, stirring, for about 1 minute or until the sauce is thickened and darkened. Stir in the buk choy.
Reduce the heat to medium; add 2 teaspoons oil. Stir-fry the ginger, garlic and chilli until softened and fragrant. Return the chicken to the wok with sauces and onions.