In a large mixing bowl add the beef and cornstarch, toss to coat. Put in the refrigerator for 30 minutes.
While the beef is in the refrigerator, make the sauce: whisk together the orange juice, orange zest, soy sauce, rice vinegar, sesame oil, and sugar.
Add the vegetable oil to a large work (or deep pan) over medium heat.
Fry the beef in batches until it has turned golden and crispy. Set aside on a paper towel-lined plate.
In the same pan add the garlic and ginger. Saute only until fragrant, about 1 minute.
To make a slurry (to help thicken the sauce), in a small bowl mix a ¼ tsp cornstarch with 2 tbsp of the sauce mixture and whisk until smooth.
Add the sauce mixture to the pan and cook until it has reduced by half. Slowly whisk in the slurry thickener. Add the beef to the pan and toss to combine.
Serve with steamed white rice and broccoli, garnish scallions and sesame seeds.