Add oats, water, milk and vanilla to the Instant Pot. Stir to combine. Secure the lid and ensure the pressure valve is set to "Sealing."
Cook on High Pressure for 2 minutes.
When cooking is complete, allow for a natural pressure release (about 10-15 minutes).
Once pressure has released, open the lid and stir the oatmeal.
Serve in bowls and top with fresh berries, a splash of milk, and maple syrup as desired.
Notes
The Natural Pressure Release (NPR) is essential if you don't want to make a big mess. If you release the pressure manually, your Instant Pot will spray out liquid and it's no fun to clean up!
You can make a batch of oatmeal in advance. Once it has been cooked, let it cool completely, transfer it to an airtight container, and then store it in the fridge for up to 5 days. This recipe can be doubled, but I don't recommend tripling it in the Instant Pot. The added liquid will make the sealing process quite messy.
To reheat, place your cooked oatmeal in a microwave-safe bowl and heat at 30-second intervals until warmed through. Add a splash of milk to loosen up the oats and add your toppings!