In a medium bowl, whisk together minced garlic, sesame oil, soy sauce, oyster sauce, rice vinegar, and corn starch until smooth. Add thinly sliced beef and let marinate for at least 10 minutes.

Bring a large pot of water to a boil and add udon noodles, cooking for 1-2 minutes until loosened. Drain and rinse under cold water.

Heat oil in a wok over medium-high heat. Add garlic and onion, stir-frying until fragrant. Add cabbage and stir-fry until wilted.

Add marinated beef into the wok and stir-fry for 2-3 minutes until browned and cooked through.

Prepare black pepper sauce by mixing remaining ingredients and adding to the wok, stirring until thickened.

Return vegetables and udon noodles to the wok, tossing to coat in the sauce. Heat through for 1 additional minute.