In a large bowl, combine the chicken pieces, soy sauce, sesame oil, garlic powder, onion powder, ground ginger, salt, and pepper. Mix well to coat the chicken evenly. Marinate for at least 30 minutes in the refrigerator for best flavor.
Preheat your griddle or grill over medium-high heat. Add the vegetable oil and allow it to heat up for a minute.
Add the marinated chicken to the griddle and cook for about 5-7 minutes, stirring occasionally, until the chicken is cooked through and has a nice sear.
Add the broccoli, bell peppers, zucchini, and mushrooms to the griddle. Stir-fry the vegetables with the chicken for an additional 5-7 minutes, or until the vegetables are tender-crisp.
Sprinkle the chopped green onions and sesame seeds over the chicken and vegetables. Toss everything together for a minute to combine flavors.
Serve hot, either on its own or over steamed rice or noodles.