Boil the noodles: Cook the lo mein noodles in a large pot of boiling water according to the package directions, pulling them a minute shy of fully tender since they'll finish in the pan. Drain, rinse under cold water, and toss with 1 teaspoon of the vegetable oil so they don't clump.

Velvet the chicken: Toss the sliced chicken with 1 tablespoon of the soy sauce and the 2 teaspoons of cornstarch until every piece is lightly coated. Let it sit while you mix the sauce.

Mix the sauce: Whisk the remaining 3 tablespoons soy sauce with the oyster sauce, dark soy sauce, brown sugar, sesame oil, chicken broth, white pepper, and the 1 tablespoon of cornstarch until no lumps remain.

Sear the chicken: Heat 1 tablespoon of the vegetable oil in a large wok or skillet over high heat until it shimmers. Spread the chicken in a single layer and cook for 4-5 minutes, stirring after the first 2 minutes, until browned and cooked through to 165°F on an instant-read thermometer. Transfer to a plate.

Stir-fry the vegetables: Add the remaining oil to the pan. Cook the garlic and ginger for 30 seconds until fragrant, then add the cabbage, carrots, and bell pepper. Stir-fry over high heat for 3-4 minutes, until the vegetables are crisp-tender and still have some bite.

Toss the chicken lo mein together: Return the chicken and any juices to the pan, add the drained noodles, and pour the sauce over everything. Toss with tongs, lifting from the bottom, for about 2 minutes until the sauce thickens and turns glossy and every noodle is coated.

Finish and serve: Stir in most of the green onions, scatter the rest over the top, and serve straight from the pan while it's hot.