Turn your Instant Pot onto the Saute setting. Add the Sesame Oil to the Instant Pot and let the oil heat up.
Add enough of the steak to cover the bottom of the Instant Pot, brown the meat, transfer the browned meat to a plate and set aside. Repeat until all meat has been browned.
Add the minced garlic and ginger to your Instant Pot and sauté it for about a minute.
Add the soy sauce, water and brown sugar to the ginger and garlic and stir until well combined. Use your spatula to deglaze the pot, making sure nothing is stuck to the bottom of the pot so you don't risk a Burn notice.
Transfer the browned beef back to the Instant Pot, close the lid and make sure the valve is in the sealing position. Use the Meat or Manual setting to cook the meat mixture on high pressure for 8 minutes.
When it's finished, use the Quick Pressure Release method. Remove the lid once the pressure is completely released. Add the chopped broccoli to the meat mixture, put the lid back on the pot and use the Low Pressure setting to cook everything for 0 minutes.
When it's finished, use the Quick Pressure Release method. Remove the lid once the pressure is completely released. The broccoli will be soft... if you want crisper broccoli, see notes below.
Turn Instant Pot onto the Saute function. Make a cornstarch slurry by whisking together the corn starch and 3 tablespoons water until it's smooth. Add the cornstarch mixture to the Instant Pot. Stir it constantly until the sauce starts to thicken (this should only take a couple of minutes).
Turn the Instant Pot Off. Add the green onions to the Instant Pot and stir for another 2-4 minutes while stirring it constantly until your onions are cooked to your desired tenderness. This will also help thicken the sauce up.
Serve your Mongolian Beef and Broccoli over cooked white rice. Drizzle with Sriracha, if desired.