In a medium bowl, toss the chicken pieces with cornstarch until evenly coated. This will help give the chicken a nice texture when cooked.
Heat olive oil in a large skillet over medium-high heat. Add the chicken and cook for about 5-7 minutes, stirring occasionally, until the chicken is golden brown and cooked through. Remove the chicken from the skillet and set aside.
In the same skillet, add garlic and ginger. Sauté for about 1 minute until fragrant.
In a small bowl, whisk together soy sauce, honey, rice vinegar, sesame oil, and red pepper flakes (if using). Pour this sauce into the skillet and bring to a simmer.
Return the cooked chicken to the skillet and toss to coat in the sauce. Cook for an additional 2-3 minutes until the sauce thickens slightly.
Serve the sesame chicken over cooked brown rice or quinoa. Garnish with sliced green onions and sesame seeds.