Combine the cornstarch, water, and salt in a bowl and mix into a batter.
Add the thinly sliced flank steak to the batter, mix until every piece is coated, and set to the side.
Heat a pot of oil to 375°F. Drop the beef in and cook until golden and crispy on the outside, then remove and let it rest.
While the beef rests, combine the orange zest, orange juice, dark soy sauce, light soy sauce, sugar, rice vinegar, garlic, and ginger in a pan and bring to a simmer.
Stir the cornstarch and cold water together and add the slurry. Once the sauce has thickened, add the beef and toss until the sauce coats every piece.
Serve over a fresh bowl of rice. Optionally garnish with sesame seeds and scallions. But it's your food, you eat it how you like.