In a mixing bowl, combine the chicken, soy sauce, teriyaki sauce, and sesame oil. Stir to coat evenly. Marinate for 15–30 minutes.
Preheat the Blackstone griddle over medium-high heat. Add 1 tablespoon of vegetable oil and heat until shimmering.
Add the marinated chicken in a single layer. Cook for 5–7 minutes, turning occasionally, until golden-brown and cooked through (internal temp 165°F). Remove and set aside.
Add the remaining 1 tablespoon of vegetable oil to the griddle. Add zucchini and onion. Sauté 3–4 minutes until tender-crisp. Season with salt and pepper. Remove and set aside.
Push the vegetables and chicken to one side of the griddle. Pour beaten eggs onto the empty side and scramble until fully cooked.
Add cold cooked rice and frozen mixed vegetables to the griddle alongside the eggs. Stir everything together and cook for 2–3 minutes until the rice is heated through and slightly crispy at the edges.
Return the cooked chicken and sautéed vegetables to the griddle. Fold everything together gently. Adjust seasoning as needed. Cook for 1 more minute to combine.
Transfer to a serving platter. Garnish with sliced green onions and sesame seeds. Serve immediately.