In a mixing bowl, combine minced garlic, sesame oil, soy sauce, oyster sauce, Chinese white rice vinegar, and a cornstarch slurry. Add the thinly sliced beef, ensuring it is well coated with the marinade. Let the beef marinate for 10 minutes.

Bring a pot of water to a rolling boil and add the udon noodles, cooking for 1-2 minutes until they're just tender. Drain and rinse under cold water.

Heat a wok or large skillet over medium heat, add oil, and stir-fry minced garlic and sliced white onion for 2 minutes. Add chopped Chinese cabbage and stir until wilted, about 3-4 minutes. Remove and set aside.

Add the marinated beef to the pan and sear for 2-3 minutes until browned and cooked through.

Whisk together any residue left in the pan with dark soy sauce, oyster sauce, ground black pepper, and water. Pour into the pan and simmer, stirring in a slurry of cornstarch until glossy.

Add the cooked udon noodles and sautéed cabbage back into the pan. Toss everything together over medium heat until noodles are coated and heated through.