Slice the flank steak against the grain into thin strips
Add the flank steak strips, green onion, teriyaki sauce, water, ginger, salt, and black pepper to pressure cooker. Stir well.
Secure lid and close the pressure-release valve
Set pressure cooker to manual/high pressure, for 5 minutes. After cooking, allow the cooker to sit for 10 minutes before releasing any remaining pressure.
Set cooker to saute/normal. Add the water and cornstarch, and stir in with pot ingredients. Cook until thickened, 2-3 minutes.
Serve over rice or noodles, or simply by itself. Top with sliced green onions and sesame seeds.