Heat vegetable oil in a large non-stick skillet over medium-high heat.
Add chicken cubes to the skillet and cook until browned on the bottom, about 3-4 minutes, then flip and continue to cook until the internal temperature reaches 165°F, approximately 3 more minutes.
While the chicken is cooking, whisk together soy sauce, water, honey, brown sugar, rice vinegar, sesame oil, minced ginger, minced garlic, and cornstarch in a small bowl to create the teriyaki sauce.
Pour the teriyaki sauce over the cooked chicken in the skillet, stirring to coat the chicken pieces. Cook for another 30-60 seconds until the sauce thickens.
Serve the teriyaki chicken warm, garnished with sesame seeds and chopped green onions if desired.