Add the water and oats to the pot and stir to combine. Close and lock the lid. For chewy oats, pressure-cook for 10 minutes on HIGH pressure. For creamier oats, pressure-cook for 13 minutes on HIGH pressure.
When the cooking cycle completes, turn off the machine. To prevent scorching, don't let it switch to the "keep warm" setting. Allow the pot to cool down and release pressure naturally, about 10 minutes. Once the pressure has fully released, carefully open the lid away from you. (Consult your pressure cooker's manual to learn how to tell when it's safe to remove the lid.)
Add 1-2 tablespoons peanut butter, ½ a sliced banana, and 1-2 tablespoons of chopped nuts to each bowl.