Begin by dicing the chicken thighs (or breasts) into 1.5-inch cubes. Place them in a large mixing bowl and set aside.
In a separate small bowl, mix together all the sauce ingredients as listed. Stir until the cornstarch is dissolved and the sauce is smooth. Set aside.
Sprinkle cornstarch over the diced chicken in the large mixing bowl. Toss the chicken until each piece is fully coated in starch, creating a light, crispy coating.
Heat the vegetable oil in a large pan over medium-high heat. Once the oil is hot, add the coated chicken pieces in batches, frying them until they turn golden brown and crisp, about 5-6 minutes per side. Remove the fried chicken pieces and place them on a wire rack or paper towel-lined plate to drain any excess oil.
In the same pan, add the diced onions and sauté over medium-high heat until they become translucent, approximately 30-45 seconds.
Pour the sauce into the pan with the onions, allowing it to simmer and thicken. Stir occasionally to ensure it cooks evenly.
Once the sauce reaches a thicker consistency, lower the heat to medium. Add the fried chicken to the pan, tossing it gently to coat every piece with the rich, flavorful sauce.
Garnish with finely chopped green onions and a sprinkle of toasted sesame seeds. Serve hot and enjoy!