For the steak: Pour about 2 inches of oil in a large heavy-bottomed saucepan and heat to 350 degrees F over medium heat.
Meanwhile, toss the steak with the cornstarch in a medium bowl. Let sit for 5 minutes and then toss again.
Cook the steak in batches until lightly browned, 4 to 5 minutes; transfer to a plate with a mesh spider and set aside.
For the sauce: Combine the chili sauce, orange juice and soy sauce in another large heavy-bottomed saucepan. Stir and simmer until the sauce thickens, 2 to 3 minutes. Add the steak to the saucepan and stir to coat in the sauce.
Serve the orange beef with cooked rice, garnish with the scallions and sprinkle with the sesame seeds.