01 - In a medium bowl, combine beef with 1 tablespoon soy sauce, 1 teaspoon cornstarch, and 1 teaspoon sesame oil. Toss thoroughly and marinate for at least 10 minutes.
02 - Whisk together all sauce ingredients in a small bowl until smooth. Set aside.
03 - Prepare lo mein noodles according to package instructions, drain thoroughly, and set aside.
04 - Heat 1 tablespoon vegetable oil in a large skillet or wok over high heat. Add marinated beef and stir-fry for 2 to 3 minutes until browned but not fully cooked. Remove and set aside.
05 - Add garlic, broccoli florets, and red bell pepper to the skillet. Stir-fry for 2 to 3 minutes until vegetables are crisp-tender.
06 - Return beef to the skillet, add cooked noodles and prepared sauce. Toss all ingredients together and cook for an additional 2 to 3 minutes until well coated and heated through.
07 - Stir in sliced green onions, then remove from heat.
08 - Plate the stir-fry and garnish with toasted sesame seeds and extra green onions. Serve immediately while hot.