In a small bowl, whisk together the 3 tablespoons soy sauce, 2 tablespoons oyster sauce, 1 tablespoon mirin, 1 tablespoon brown sugar, 1 tablespoon Worcestershire sauce, and 1 teaspoon sesame oil. Set it within reach of the stove, since this dish moves fast.

Prepare the 14 ounces udon noodles according to the package directions. If using fresh or frozen udon, a quick soak or blanch in hot water is enough to loosen them. Drain and set aside.

Heat 1 tablespoon of the vegetable oil in a large skillet or wok over high heat until it shimmers. Add the 1 pound sliced beef in a single layer and sear for 2 to 3 minutes, until browned but not fully cooked through. Transfer it to a plate.

Add the remaining 1 tablespoon oil to the pan. Add the sliced onion, 2 cups cabbage, julienned carrot, and sliced red bell pepper. Stir fry for 3 to 4 minutes, until crisp tender and starting to char at the edges.

Add the 3 cloves minced garlic and 1 tablespoon grated ginger and stir for 30 seconds, until fragrant.

Return the beef to the pan, then add the udon noodles and pour in the sauce. Toss everything together for 1 to 2 minutes, until the noodles are hot and coated in the glossy sauce.

Stir in most of the green onions, then serve topped with the remaining green onions and the 1 tablespoon sesame seeds.