Begin by adding 1 tablespoon of soy sauce, the rice wine, 1 teaspoon of cornstarch, and the black pepper to a bowl. Whisk ingredients together until evenly combined, then add steak strips to marinate. Set aside. We recommend doing this step ahead of time so steak can marinate at least 15 minutes. Do not marinate more than 30 minutes.
Warm 2 teaspoons of sesame oil in wok over high heat then add beef and marinade. Cook for three minutes on side one, then flip and cook for another two minutes. Remove meat and set aside.
In same wok, combine peppers and onion and cook for four minutes, stirring occasionally. Add garlic and cook for one more minute.
While that's in progress, in a small bowl, mix rest of soy sauce, remaining cornstarch, and 1/2 a tablespoon of water in bowl. Add to wok after the garlic cooks for one minute.
Then, add beef back into wok along with red pepper flakes. Cook for another minute or two or until sauce has thickened to your tastes. Serve over white rice and garnish with sesame seeds and sliced green onions.