In a large pot of boiling salted water, cook the udon noodles according to package instructions until tender. Drain and set aside.
In a small bowl, combine soy sauce, honey, sesame oil, and rice vinegar. Mix well to create your teriyaki sauce.
Heat 1 tablespoon of vegetable oil in a large skillet or wok over medium-high heat. Add the sliced beef and stir-fry for 3-4 minutes until browned and cooked through. Remove beef from the skillet and set aside.
In the same skillet, add the remaining tablespoon of oil. Add the minced garlic and ginger, sautéing briefly until fragrant. Then, add the bell pepper and broccoli, cooking for about 5 minutes or until the vegetables are tender-crisp.
Return the cooked beef to the skillet along with the drained udon noodles. Pour the teriyaki sauce over everything, tossing to coat all ingredients well. Stir-fry for another 2-3 minutes until heated through and well mixed.
Remove from heat and sprinkle with sliced green onions and sesame seeds.
Notes
Feel free to customize the vegetables based on your preference.