Scrub squash clean and carefully pierce all over with a small sharp knife (10 to 15 cuts, about a half inch deep).
1 spaghetti squash, scrubbed clean
Place metal wire rack or steamer basket in the bottom of the pressure cooker. Pour in 1 cup water. Place squash on the rack or in the steamer basket.
1 cup water
Secure lid, turn valve to seal if necessary, and set for Pressure cook, 20 minutes (or Manual, High Pressure, depending on your model). It will take approximately 10 minutes to pressurize, depending on the size of the squash.
When the timer goes off, quick release the pressure by turning the valve to vent. Once the pressure has completely released, carefully remove the lid.
Remove the squash from the Instant Pot, and put it on a cutting board or platter. Allow the squash to cool long enough to handle.
Cut the squash half. If you cut it lengthwise from stem to end, you’ll have shorter "spaghetti" strands. If you cut it crosswise, you’ll have longer strands. Remove seeds. Use a fork to separate the squash into strands. You can either remove the strands from the shell or leave them in the shell to serve.
Serve as a side dish or with your choice of sauce.
Notes
Spaghetti squash size: I have a 6 qt. Instant Pot and when we tested this recipe, we used a 3.75 lb. squash. It just fit so keep that in mind when purchasing your squash. A smaller squash would be fine (reduce cooking time slightly) but if you have a larger squash, you probably won't be able to put the lid on the Instant Pot.
Storage: Cooked spaghetti squash will keep for about a week stored in an airtight container in the refrigerator. You can freeze cooked spaghetti squash (see the post above for specific instructions).