Marinate the beef in soy sauce and cornstarch for 15-30 minutes.
Heat vegetable oil in a large skillet over medium-high heat.
Add the marinated flank steak to the skillet in a single layer.
Remove beef from the skillet and set aside, leaving the drippings.
Add minced garlic, ginger, and green onions to the skillet.
Stir in the cabbage and cook until wilted but still crisp.
Combine soy sauce, hoisin sauce, brown sugar, and some water in a bowl.
Return the beef to the skillet and pour the sauce over everything.
Serve warm, garnished with extra green onions.