Add steel cut oats and water (or dairy-free milk) to the Instant Pot and stir to prevent sticking. Pressure cook on high for 20 minutes (it will take about 8 minutes for the Instant Pot to pressurize before cooking begins).
Once the timer goes off, allow to naturally release for 10 minutes, then release any remaining pressure. Carefully remove lid once steam has fully escaped.
Enjoy immediately with toppings of choice. Store cooled leftovers in the refrigerator up to 5 days or in the freezer up to 1 month. Reheat on the stovetop, stirring frequently and adding more liquid, if needed, to thin.
*Nutrition information is a rough estimate calculated without optional ingredients. *Total time includes active cook time, release time, and the time it takes for the Instant Pot to heat up (~8 minutes).