Preheat the oven to 375°F (190°C) and grease a 9x13-inch casserole dish.

Toss the diced chicken with 1/2 cup teriyaki sauce, garlic powder, salt, and pepper. Let marinate for 5 minutes.

Heat vegetable oil in a skillet, then cook the marinated chicken for 5-7 minutes until browned.

Prepare the instant rice according to package instructions.

In the casserole dish, combine the cooked chicken, prepared rice, frozen vegetables, and remaining teriyaki sauce. Stir until well mixed.

Cover the dish with foil and bake for 20-25 minutes until the vegetables are heated through.

Garnish with sesame seeds and sliced green onions before serving.