Heat 2 Tbsp. of oil in a wok over medium heat. Once nice and hot, begin to sear the flank steak in batches, about 1 minute each side or until crisp and golden.
Add the beef back into the wok, toss to coat in the sauce. Add in the green onions and dried red chilies. Cook until sauce thickens and becomes glossy, about 3-4 minutes.