Preheat a large skillet or hibachi grill over medium-high heat.
Add vegetable oil or sesame oil to the pan.
Add onions and carrots first and sauté for 2–3 minutes.
Add broccoli, bell peppers, zucchini, and mushrooms. Stir-fry for another 5–6 minutes until vegetables are tender-crisp.
Sprinkle garlic powder, black pepper, and soy sauce over vegetables. Stir well to coat evenly.
Cook for another 1–2 minutes, then remove from heat.
Optional: Garnish with sesame seeds before serving.
Serve hot as a side dish with rice or protein.