Add the steak to a large, resealable plastic bag, or a 9x13” baking dish. Whisk together the soy sauce, sherry, olive oil, and brown sugar. Add the smashed garlic pieces and the slices of ginger. Pour the marinade over the steak and turn to coat. Stick the steak in the refrigerator and let marinate for 2 to 24 hours (I always like around 4 hours). If you’re using a plastic bag, set it in a mixing bowl. It probably won’t leak, but if it does and you didn’t put it in a bowl, well… yeah.
Preheat your outdoor or indoor grill pan to its highest heat setting. Let it get good and screaming hot. Remove the steak from the marinade and let the excess drip off. Discard the liquid and solids in the bag or baking dish. Season the steak with salt and pepper. Grill the steak 3 to 4 minutes per side for medium-rare. Use a meat thermometer to be 100% sure. If you like it more well done, you’re on your own.
Once the steak is done, remove it to a cutting board, tint it with aluminum foil, and let rest for 10 minutes. Slice the steak against the grain into thin strips. Neatly layer it onto a platter and liberally drizzle that crema all over it. Garnish with crumbled feta, tomatoes, and a scattering of scallions. Enjoy!