Slice the spaghetti squash in half and then scoop out the seeds in the center.
Place a trivet or steamer basket in the bottom of the Instant Pot and add a cup of water into the bottom. Arrange the cut squash halves on top of the trivet and secure the lid. Make sure the steam release valve in the lid is turned to the Sealing position.
Use the pressure cook or manual button to set the pressure cooker to cook at high pressure for 7 minutes. It will take roughly 8-10 minutes for the pot to build pressure before the cooking cycle begins, so make sure to consider that extra time when planning your meal.
When the timer goes off, carefully turn the steam release valve to Venting, to quickly release any remaining steam pressure. (Make sure your hand isn't over the vent, so that you don't get burned by the steam.)
When the floating valve in the lid drops, it's safe to remove the lid. Use a fork to check the squash to make sure it's cooked to your liking. I like my squash to be tender, but not mushy. If there is water collected in the center of your squash, drain it before serving.
To serve the squash, use the tines of a fork to separate the cooked strands into spaghetti-like pieces and remove them from the hard shell. Use the cooked squash in your favorite recipe and store leftovers in an airtight container in the fridge for up to a week.