Heat the Oil:In a large skillet or wok, heat the vegetable oil over medium-high heat until shimmering.
Sauté the Veggies:Add the mushrooms, broccoli, baby corn, bell pepper, snap peas, zucchini, and carrots. Stir frequently and cook for 5–6 minutes, until the vegetables are bright and tender-crisp.
Make the Sauce:In a small bowl, whisk together soy sauce, sesame oil, garlic, ginger, brown sugar (or honey), and red pepper flakes if using. In another small bowl, dissolve the cornstarch in the cold water to form a slurry.
Combine Sauce and Veggies:Stir the cornstarch slurry into the sauce, then pour the sauce over the cooked vegetables in the skillet. Toss to coat everything evenly.
Thicken and Finish:Bring the mixture to a gentle simmer and cook for another 5 minutes, until the sauce thickens and the vegetables are fully coated and tender.
Serve:Remove from heat and top with sliced green onions. Serve immediately as-is or over rice or noodles.