Heat peanut oil in a large stockpot or Dutch oven over medium heat.
In a large bowl, combine steak and 2 tablespoons cornstarch, tossing to coat and letting the steak absorb the cornstarch. Add remaining 2 tablespoons cornstarch before adding to the stockpot.
Working in batches, cook steak until golden and crisp, about 2-3 minutes. Transfer to a paper towel-lined plate.
In a medium saucepan over medium high heat, combine soy sauce, brown sugar, orange juice, vinegar, garlic, ginger, Sriracha and sesame oil until slightly thickened, about 1-2 minutes. Stir in steak and gently toss to combine.
Serve immediately, garnished with sesame seeds and green onion, if desired.