Cut the chicken into bite-sized pieces. Coat them lightly in corn starch. Heat the oil and fry the chicken until it's cooked through, and slightly crispy on the outside. Remove to a plate.
Add more oil if you need to, and fry onion and carrot on fairly high heat for one minute. Add garlic, sugar, vinegar and worcestershiresauce and cook for a few minutes until the sugar has melted. Add the chicken to the pan and stir until it's well coated. Season with some black pepper and salt if you wish, and serve it with rice.