Warm 1 tablespoon of vegetable oil in a wok or large skillet over medium-high heat.
Add the thinly sliced onion and sauté until it softens, about 3 to 4 minutes.
Stir in the minced garlic and cook for an additional minute until fragrant.
Toss in the carrots and shredded cabbage, then drizzle with the remaining tablespoon of vegetable oil.
Stir and cook the vegetables for several minutes until they start to soften.
Add the sliced mushrooms and cook everything together for 2 to 3 minutes.
Pour the shaoxing wine into the pan and mix well to combine.
Add the cooked lo mein noodles along with 2 tablespoons of the reserved pasta water.
Sprinkle in the dark soy sauce, light soy sauce, hoisin sauce, oyster sauce, sugar, and salt.
Toss all ingredients thoroughly and taste; adjust seasoning if needed.
Finally, fold in the sliced scallions and give everything one last good stir.
Serve immediately and enjoy your homemade Vegetable Lo Mein while it’s hot.