Add all sauce ingredients to a small bowl and whisk to combine. Set aside.
Heat 1 tablespoon of oil in a large skillet over medium heat. Once the oil is heated, add the chicken chunks. Season with salt and pepper and cook until the chicken is fully cooked and browned, about 8-10 minutes. Once cooked, remove the chicken and set aside.
In the same skillet, add 1 tablespoon of oil. Add the veggies and stir-fry for about 8-12 minutes, or until the vegetables are tender-crisp and vibrant.
Return the cooked chicken to the pan with the vegetables. Pour the prepared sauce over the chicken and vegetables. Stir everything together until the sauce thickens and coats the chicken and veggies, about 2 minutes. If the sauce becomes too thick, add a little water to achieve the desired consistency.
Remove from heat and garnish with sesame seeds and green onions, if desired. Serve the stir-fry over cooked rice or noodles, or enjoy it on its own.
