Cut the chicken into bite-size, then combine the chicken with cornstarch. Toss to coat.
In a large skillet over medium-high heat, heat the cooking oil and add the chicken, garlic, and ginger. Cook and stirring occasionally until the chicken turn lightly browned.
Add the bok choy and continue cooking, tossing or stirring constantly for about a minute, just until the bok choy is wilted. Add the soy sauce, sugar, salt, and pepper and toss well to coat. Cook for about 2 minutes, just until the sauce thickens. Once the sauce is thickens, turn off the heat.
Serve with warm rice. Enjoy!