Slice the flank steak into thin strips, cutting against the grain.
Place the steak and cornstarch in a large zip-top bag. Seal and shake until the beef is evenly coated.
Transfer the coated steak to the Instant Pot. Add the minced garlic, soy sauce, water, brown sugar, and shredded carrots. Stir to combine.
Secure the lid and set the valve to the Sealing position.
Cook on High Pressure for 8 minutes.
When the cooking time is complete, allow the pressure to naturally release for 10 minutes. Then carefully perform a quick release to release any remaining pressure.
Stir the beef and sauce until well combined.
Serve hot over cooked rice and garnish with sliced green onions and sesame seeds, if desired.