For the beef: Heat a wok over high heat and fill halfway up with peanut oil. Heat the oil to 350 degrees F, or until a cube of bread turns golden brown in 15 seconds and floats to the surface.
Place the beef strips in a large bowl and add 2 tablespoons cornstarch. Toss until the beef has absorbed the cornstarch. Add the remaining 1 tablespoon cornstarch right before frying and toss to coat.
Fry the beef in 2 to 3 batches until golden, 4 to 5 minutes. Drain on paper towels and season with sea salt.
For the sauce: Set another wok or saute pan over high heat and add the soy sauce, chili sauce and orange juice. Bring to a simmer and cook until it becomes thickened and coats the back of a spoon, 1 to 2 minutes. Toss the beef in the sauce to coat thoroughly.
Serve over a bed of the shredded lettuce and sliced cucumber that has been sprinkled with rice vinegar. Then garnish with the scallions and orange zest.