In a medium mixing bowl, combine beef and marinade ingredients. Let marinate for at least 30 minutes or up to overnight, covered in the fridge.
In a small bowl, combine sauce ingredients and set aside. Set aside.
In another small bowl, dissolve 1 tablespoon cornstarch in 1 tablespoon cool water to make a slurry. Set aside.
In a wok or large frying pan on medium high heat, add 2 tablespoons vegetable or canola oil. Add half the beef and stir fry until 70-80% cooked. Remove and set aside. Add 1 tablespoon vegetable or canola oil and repeat with remaining beef. Remove and set aside.
Add 1 tablespoon vegetable or canola oil, if needed. Add ginger, stir fry for 30 seconds. Add onion and stir fry for another 2 minutes. Add garlic and stir fry for another 30 seconds, until fragrant.
Add the sauce. When the sauce is heated through, stir in the slurry. Add all the cooked beef along with the drippings and cook until the sauce starts to simmer and thicken, and meat is cooked through, about another 1-2 minutes. Turn off the heat. Drizzle in sesame oil.
Transfer onto a serving platter. Garnish with green onion and roasted sesame seeds.