In a large bowl, beat together the eggs, salt, and several grinds of black pepper. Fold in the chopped broccoli, green onions, and cheddar cheese.
Grease a 7-inch pan, then pour the egg mixture into it. Pour 1 cup of water into the bottom of your Instant Pot and place a trivet over that to keep the pan above the water.
Place the pan with the frittata mixture on top of the trivet and secure the lid. Move the steam release valve to Sealing. Use the Pressure Cook or Manual button on your machine to cook at high pressure for 10 minutes.
When the cooking cycle is complete, let the pressure naturally release for 10 minutes. Once the screen reads LO:10 you can move the steam release valve to Venting to release any remaining pressure.
Use oven mitts or a tea towel to carefully remove the frittata pan. If you see a little liquid on top of the baked eggs, don't freak out! The water will evaporate quickly as your egg bake cools.
Slice the frittata into 4 slices and serve warm. Leftovers can be stored in an airtight container for up to 5 days in the fridge.