Cut 3 lb. spaghetti squash lengthwise and scoop out seeds.: You will notice a firm, pale interior that yields slightly under pressure when the squash is ripe; the seeds nestle in a fibrous pocket that smells mildly sweet when exposed. Use a sturdy chef's knife and a towel under the squash to stabilize it, pressing down with steady force until you slice through. Scoop out the seeds and pith with a spoon, which prevents excess moisture from steaming the flesh later. A common mistake here is trying to cut a slippery squash without support, which can be dangerous, so always secure it first.
Add 1 cup of water to the Instant Pot.: The small pool of water creates steam that cooks the squash evenly and quickly, producing tender strands. Pour with care to avoid splashing the lid sealing ring, and double check that the insert is properly seated. If you skip liquid, the pressure cooker will not build steam and the squash will remain firm. You should hear the gentle hum as pressure builds, signaling the cooking environment is set.
Stack the spaghetti squash on top of each other (cut-side up).: Positioning the halves cut-side up allows steam to penetrate directly into the flesh, softening it uniformly. Arrange them so they are stable, and if they wobble, tuck a rolled towel beneath the halves to stabilize. This orientation reduces the chance of one side overcooking and the other remaining firm. If placed cut-side down, the top may stay too firm and resist shredding.
Close the lid and make sure the knob is turned to sealing.: Hearing the valve click into place gives you confidence that the Instant Pot will trap the steam. Ensure the silicone gasket is clean and properly seated, because a misaligned gasket can prevent pressure from building. If the lid does not seal and pressure fails to accumulate, the squash will steam rather than pressure cook, extending the time and producing a different texture.
Set to manual high-pressure for 10 minutes (increase if your squash is larger than 3 lb.): Ten minutes at high pressure typically yields tender, shreddable strands for a 3 lb. squash, and the steam will perfume the kitchen with a sweet squash aroma. If your squash is noticeably larger, add a few extra minutes to ensure the center softens. The mistake here is underestimating size; an undercooked center will resist forming noodle like strands and feel dense when shredded.
When the timer goes off, turn the vent on the top of the lid to venting to release the steam.: As you carefully flip the valve to venting, you will see a gust of steam and feel heat; use a long utensil or towel to protect your hand. This quick release reduces carryover cooking but you must do it responsibly to avoid burns. Do not place your face over the valve, and keep children away during venting, since the steam is intensely hot.
Once the venting knob has dropped, open the lid and shred the spaghetti squash with two forks to turn squash into spaghetti-like noodles!: The first impression is a puff of warm, sweet squash aroma and delicate strands that pull away with little resistance; use two forks in opposite directions to tease out long noodles. Visually, you want thin, separated strands rather than clumps, and the texture should be tender yet slightly toothsome. If pieces are still dense, you may return the halves to the Instant Pot for a couple more minutes, as undercooked squash will create gummy clumps rather than separate strands.