Toss the chicken in the cornstarch to coat, shaking off any excess. Set aside.
Heat oil in a large skillet over medium-high heat. Add the chicken to the heated skillet and cook for 5-7 minutes, or until the chicken is golden brown and cooked through (internal temperature should reach 165°F). Remove chicken to plate and set aside.
Add the remaining ingredients to the skillet and cook for 2-3 minutes, or until the sauce slightly thickens. Return the chicken to the pan, toss to coat with the sauce, and cook for another minute.
Remove from heat and top with sesame seeds. Serve immediately, over rice if desired.
Notes
Store leftovers in an airtight container for up to 3 days. Reheat covered in the oven or over medium-low heat in a skillet.