Use top round or sirloin; thinly slice and cut into ½” x 2” strips. Pat meat dry. Heat oil in wok over medium-high heat. Add garlic and stir-fry until lightly golden. Add chilies, green onion and ginger and stir-fry 1 minute. Add beef and stir-fry until just browned, about 1 minute. Blend in lime juice, fish sauce and sugar. Arrange in heated dish. Sprinkle with cilantro.