In a bowl, combine chicken, 1 tablespoon of the cornstarch, 2 tablespoons of the soy sauce, and 1 tablespoon of the vegetable oil. Massage meat to fully coat and marinate for about 10 to 15 minutes.
In a bowl, combine chicken broth, the remaining 2 tablespoons soy sauce, rice vinegar, sesame oil, brown sugar, chili garlic paste, and the remaining 2 tablespoons cornstarch. Whisk together until blended. Set aside.
In a wok or a wide, thick-bottomed pan over high heat, heat the remaining 2 tablespoons canola oil. Add chicken and cook, turning as needed, until lightly browned. With a slotted spoon, remove chicken from the pan and drain on paper towels. Keep warm.
Add sauce mixture to the pan and bring to a boil, whisking vigorously to prevent lumps. Cook, whisking regularly, until thickened.
Add chicken and continue to cook for about 3 to 5 minutes or until heated through.
Remove from pan and transfer onto a serving platter. Garnish with sesame seeds and green onions, if desired. Serve hot.