1With a sharp knife, cut beef into shreds (this is best done if meat is partially frozen). Combine 1 TB soy sauce, 1 TB of the cornstarch, baking soda and 1 tsp of the sesame oil in a zip-lock-type bag. Add the meat and toss to coat. Refrigerate for 1-3 hours.
2In a small bowl, combine orange juice concentrate, remaining soy sauce, rice vinegar, sugar and remaining cornstarch. Mix well and set aside.
3Heat the oil in a wok or large skillet over high heat. Add the garlic, ginger orange zest and pepper flakes. Stir fry until the mixture is fragrant (1 minute).
4Add the beef, reserving the sauce, and stir fry for a few minutes, until the beef is browned. Add the reserved sauce and stir well. Cook and stir until the mixture comes to a boil and thickens. Splash on the remaining sesame oil and serve.