Cook the spaghetti. Boil in salted water until just al dente. Drain and rinse briefly under cool water to stop cooking. Toss with a drizzle of oil to prevent sticking.

Prep the sauce. In a bowl, whisk soy sauce, oyster or hoisin, rice vinegar, sesame oil, and brown sugar or honey. Add chili sauce if you like heat. If you want a thicker glaze, stir in the cornstarch slurry.

Heat the pan. Set a large skillet or wok over medium-high to high heat. Add 1 tablespoon oil and swirl to coat. You want it hot before anything hits the pan.

Sear the protein (if using). Season lightly with salt and pepper. Stir-fry until just cooked through and browned at the edges, 2–4 minutes. Transfer to a plate.

Stir-fry aromatics. Add the remaining oil. Toss in garlic, ginger, and scallion whites. Stir for 20–30 seconds until fragrant—don’t let them burn.

Cook the vegetables. Add the harder veggies first (carrots, broccoli), stir 1–2 minutes. Then add quicker-cooking ones (bell pepper, snap peas, mushrooms, cabbage). Cook until crisp-tender, about 3–5 minutes. Season with a pinch of salt.

Combine everything. Return the protein to the pan. Add the cooked spaghetti. Pour in the sauce. Toss over high heat for 1–2 minutes until the noodles are well-coated and glossy. If it looks dry, splash in a bit of water or stock.

Finish and serve. Turn off the heat. Sprinkle with scallion greens and sesame seeds. Taste and adjust with a squeeze of lime, extra soy, or more chili. Serve hot.