Add the beef and cornstarch to a medium bowl (or a plastic bag) and toss to combine. Allow the beef to sit at room temperature for at least 15 minutes – this will bring the beef to room temperature and help tenderize the meat.
In a small bowl, whisk together the soy sauce, water, light brown sugar, garlic, ginger, and red pepper flakes.
Heat the Instant Pot using the Saute function and add the olive oil. When the oil is hot, add the beef (feel free to cook the beef in batches– you don’t want to overcrowd the pot). Sear the beef for 2 minutes and then flip it and sear for an additional 2 minutes.
Add the sauce to the pan and stir to combine the sauce and beef.
Place the broccoli on top of the beef but do not mix it into the sauce!
Attach the lid and ensure the valve is in the sealing position. Set the Instant Pot to Pressure Cook Manual for 1 minute.
Garnish with green onion and sesame seeds. Serve immediately and store any leftovers in an airtight container in the fridge for up to three days.