In a medium bowl, whisk together the soy sauce, vinegar, sesame oil, and sugar. Pour half the mixture over the chicken, along with half the ginger and half the garlic. Let the chicken sit for 20 minutes to marinate.
Heat a large pan over high heat, add 1 teaspoon of olive oil to the pan and add the chicken. Cook, stirring constantly, for about 3 minutes, then remove the chicken from the pan and transfer onto a plate. Set aside.
Add the remaining olive oil to the pan. Add the bok choy and cook 1 minute. Then add in the leeks, bean sprouts and chilli flakes. Cook, for a further minute until the bok choy and leeks are tender.
Stir in the rest of the marinade and season with salt. Move the vegetables to one side of the pan. Add the remaining ginger and garlic to the centre of the pan and cook for 30 seconds, until fragrant.
Return the chicken to the pan and combine with the rest of the ingredients. Heat for 1 furthermore minute and then take off the heat. Serve immediately.
Serving suggestion: