Thinly slice the green onions and set aside. Cut chicken into 1-inch pieces. Combine the chicken, salt, cornstarch, and water in a medium bowl. Set mixture aside.

Peel and finely grate the ginger using a hand-held rasp-style grater or box grater. Transfer ginger to a small mixing bowl. Grate or mince the garlic. Add it to the ginger with the gochujang, mirin, honey, sesame oil, and vinegar, and stir until well combined. Set sauce aside.

Heat a large, heavy-bottomed frying pan over medium-high heat. Once hot, add the oil, swirling to coat bottom of pan. Add the chicken and spread pieces into a single layer. Cook until well-browned on underside, 2-3 minutes. Turn pieces over and cook until browned on second side, 2-3 minutes. Transfer chicken to a bowl.

Reduce heat to medium-low and add sauce mixture to pan. Cook, stirring constantly, until hot, about 30 seconds. Return chicken to the pan and toss until well coated.

Transfer chicken to a serving plate. Sprinkle with the sesame seeds and green onions, and serve immediately.