Preheat a wok or pan at high heat. Add the oil and the chicken, only enough to fill the base of the pan. Let it get golden on one side without moving it around. Flip it and repeat al all sides. Remove the chicken and continue with the rest of the cubes if there's more.
Add half the soy sauce, vinegar and oyster sauce and let it bowl with the chicken until it thickens. Remove everything from the wok.
Add a bit more oil and the veggies. Sautée them until they are golden and start to become soft, about a minute. Add the rest of the soy sauce, vinegar and oyster sauce and let it boil until the sauce thickens.
Mix the chicken with the veggies and garnish with the green part of a spring onion (sliced) or coriander.