In a mixing bowl, combine soy sauce, oyster sauce, dark soy sauce, mirin, brown sugar, and pepper. Whisk until smooth and set aside.

Heat a large frying pan over medium heat and add sesame oil. Once hot, sauté minced garlic and diced onion for 1-2 minutes.

Push garlic and onion to one side of the pan. Add ground pork and cook for 1-2 minutes, breaking it apart until browned.

Stir in cabbage, carrot, and mushrooms. Cook for another 2-3 minutes until veggies are tender but still crunchy.

Add cooked udon noodles and prepared sauce to the pan. Toss everything together for 1-2 minutes to combine.