Prepare the sauce: In a bowl, whisk together hoisin sauce, soy sauce, rice vinegar, honey, chili flakes, and cornstarch slurry. Set aside.
Heat the pan: Place a large wok or skillet over high heat. Add the oil and allow it to get hot before adding vegetables.
Cook aromatics: Add sliced onion, garlic, and ginger. Stir fry for 1 minute until fragrant.
Add hard vegetables: Add broccoli, carrots, and bell peppers. Stir fry for 4 minutes while tossing constantly.
Add softer vegetables: Add zucchini, mushrooms, cabbage, snap peas, and baby corn. Cook for another 4 to 5 minutes until tender-crisp.
Add the sauce: Pour the hoisin mixture into the pan. Toss everything together until the vegetables are evenly coated.
Simmer briefly: Let the sauce bubble for 2 minutes until it thickens and becomes glossy.
Taste and adjust: Add salt or pepper if needed. If you like extra sweetness, stir in a little more hoisin sauce.
Serve: Garnish with sesame seeds and green onions. Serve hot over rice or noodles.