Thinly slice meat across the grain into ¼-inch-thick slices.
Place beef in a large resealable plastic bag set in a shallow dish.
Combine soy sauce, rice wine, tangerine juice, ½ of the tangerine zest, sesame oil, cornstarch, garlic and crushed red pepper in a small bowl and whisk to mix.
Pour marinade over beef in bag; seal bag. Marinate in the refrigerator for 2 hours (or longer)
Remove beef from marinade, discarding the marinade.
Dredge the pieces of meat individually in of cornstarch until lightly coated,
Heat oil in a clean wok or saute pan over high heat.
Just before the oil starts to smoke, spread the flank steak pieces evenly in the wok, and let sear for 1 minute.
Flip the steak over and let the other side sear for another 30 seconds, then transfer to a sheet pan, tilting it slightly to let the oil drain. The beef should have a crusty coating.
Drain most of the oil from the pan. leaving about 1 tablespoon in the pan.
Heat over medium-high.
Add ginger and garlic to pan stir frying for about 15 seconds.
Add the soy sauce, tangerine juice, water and brown sugar. Bring the sauce to a simmer, stirring occasionally.
Let the sauce simmer for 1 minute, then slowly stir in the cornstarch slurry mixture–until the sauce coats the back of a spoon. Add the beef and tangerine segments
Toss everything for another 30 seconds until all of the beef is well-coated.
There should be almost no liquid, as the sauce should be clinging to the beef.
If the sauce is too thick, add a little bit of hot water to thin it out.
Serve over Jasmine Rice or your favorite Asian Noodles
Garnish with scallions and cilantro.
**There should be almost no liquid, as the sauce should be clinging to the beef. If you have too much sauce, increase the heat slightly and continue cooking until thickened. If the sauce is too thick, add a little bit of hot water to thin it out.