Chill the steak in the freezer for 30 minutes before you slice it, this will make it easier to cut in thin slices. Slice the steak first crosswise in 1/2-inch thick slices. The cut each slice lengthwise into strips.
2. Marinate the beef:
In a medium bowl, whisk together the marinade ingredients; the soy sauce, vinegar, grated ginger, honey, red chile flakes, and cumin. Mix the beef in with the marinade to coat and let it sit for at least 30 minutes, and up to 4 hours, in the fridge.
3. Make cornstarch slurry:
In a small bowl, mix the cornstarch with 2 tablespoons of cold water to make a slurry.
4. Brown the beef strips:
Heat the oil in a wok (vegetable oil plus dark sesame oil if using), or a large sauté pan, over high heat until it is nearly smoking. As the oil is heating up, pat the beef dry and separate it into small batches no larger than what can fit into the palm of your hand. Working in batches, sauté beef until just brown outside but rare inside, no more than 1 minute. Transfer beef to a bowl.
5. Stir fry chilies, garlic, ginger:
When all of the beef is cooked, put the chilies and garlic into the pan and stir-fry 30-45 seconds. Add the julienned ginger and cook for 30-45 seconds more.
6. Add beef, cornstarch slurry, scallions:
Add the beef back to the pan. Add the cornstarch slurry. Add the scallions and mix everything together. Cook for 1 minute.
7. Remove from heat, stir in cilantro:
Turn the heat off and mix in the cilantro. Serve at once with steamed white rice.