Soy, ginger, and garlic makes the marinade for this steak distinctly flavorful.
Peel half the ginger; finely grate to make 1 tablespoon. Thinly slice remaining half. Scatter half grated and sliced ginger, garlic, brown sugar, cinnamon, and cinnamon sticks, if using, in a nonreactive baking dish. Cut steak against grain into three 6-inch pieces; place in dish. Scatter with remaining dry ingredients. Pour sherry, soy sauce, and olive oil over the steak. Marinate, turning meat several times, for 30 minutes, or refrigerate several hours.
Heat broiler. Season steak with salt and pepper; transfer to broiler pan. Broil until brown and just charred, about 4 minutes. Turn; broil about 3 minutes for medium rare. Transfer to cutting board. Let rest 5 minutes. Cut into thin strips. Top with cilantro, if using; serve.
Flank steak can also be used in this recipe, but broil it a few minutes longer as it is slightly thicker than skirt steak, which is long and flat.