Pierce the steak with a fork several times on each side. Remove a 2-inch strip of zest from the tangerine, halve the fruit and squeeze the juice into a resealable plastic bag. Add the zest, scallions, soy sauce, sesame oil, sugar, ginger, garlic, pepper flakes and 1/4 cup water to the bag and mix well. Add the meat, seal the bag and turn to coat. Refrigerate overnight.
Preheat the broiler with a broiler pan in place. Remove the steak from the bag and reserve the marinade. Pat the meat dry and place on the preheated broiler pan. Cook, without turning, until the meat is golden brown and a thermometer inserted in the thickest part registers 130 for medium-rare, about 10 minutes. Let rest 5 to 10 minutes before slicing; reserve the drippings.
Meanwhile, boil the marinade in a small pot over medium-high heat until slightly thickened. Stir in the orange preserves and the drippings from the meat. Slice the meat against the grain and top with scallions. Serve with the sauce.