Wash all vegetables. Cut broccoli into bite-sized florets. Peel and slice carrot thinly on a diagonal or use a peeler to create ribbons so they cook quickly. Core and chop red bell pepper into strips about 1/2-inch wide. Trim ends of snow peas. Slice mushrooms. Thinly slice onion. Mince garlic and ginger. Slice green onions separating white and green parts.

In a small bowl, whisk together soy sauce, oyster sauce, rice vinegar, brown sugar, cornstarch and 3 tablespoons water until smooth. Add red pepper flakes, salt, and black pepper. Set sauce aside.

Cooking

Heat the wok or pan

Place a large wok or heavy-bottomed skillet over high heat. When hot, add 2 tablespoons neutral oil and swirl to coat. Heat until shimmering but not smoking (about 30–45 seconds).

Aromatics

Add the white parts of the green onions, minced garlic and minced ginger to the hot oil. Stir-fry for 20–30 seconds until fragrant, stirring constantly to prevent burning.

Cook hard vegetables

Add the carrots and broccoli florets. Stir-fry briskly for 2 minutes, tossing constantly so they get bright and slightly blistered but remain crisp. If the pan becomes dry, add a splash (about 1 tablespoon) of water and cover with a lid for 30–45 seconds to create steam and help cook through, then uncover and continue stirring.

Add remaining vegetables

Add the red bell pepper, snow peas, mushrooms and sliced onion. Continue stir-frying for another 2–3 minutes until vegetables are fork-tender-crisp. Keep them moving in the pan so they cook evenly.

Add sauce and finish

Give the prepared sauce a quick stir and pour it over the vegetables. Stir constantly; the cornstarch will thicken the sauce within 30–60 seconds, coating the vegetables. Drizzle 1 teaspoon toasted sesame oil over the vegetables and toss to combine. Taste and adjust seasoning with more salt, soy sauce, or a pinch of sugar if needed.

Turn off the heat. Sprinkle with green parts of the sliced green onions and toasted sesame seeds. Serve immediately with lime or lemon wedges on the side if using.