In a small bowl, combine half the orange zest, all of the orange juice, garlic, and soy sauce. In a separate bowl, create a slurry by mixing the cornstarch with one tablespoon of cold water. Add slurry to the juice mixture and combine.

Heat a generous drizzle of oil in a large wok or skillet over high heat. Season beef with salt and pepper. Sear beef (in batches if necessary) on all sides, about 3 to 5 minutes, and transfer to a plate.

Pour juice mixture into skillet, scraping the bottom of the pan to deglaze. Boil until the sauce begins to thicken, about 1 minute. Return beef to skillet, add orange segments and green onions, and toss until coated and heated through. Sprinkle with sesame seeds and serve with steamed rice.