Turn Instant Pot to saute mode and add the ground turkey or ground beef. Cook, crumbling with a spoon, until browned. Turn Instant Pot off.
Add the Italian seasoning, garlic powder, salt, pepper and water. Stir until well combined, scraping up any browned bits from the bottom of the pot.
Break the spaghetti noodles in half and lay them in the pot in about 6 parts, with each part laying in a different direction (this is to prevent the spaghetti from sticking together).
Pour the marinara sauce over the spaghetti. Do not stir.
Seal Instant Pot lid and turn the steam valve to the sealing position.
Cook at high pressure/manual for 5 minutes if using whole wheat spaghetti with a package cook time of 7-9 minutes. Cook at high pressure/manual for 7 minutes if using regular white spaghetti with a package cook time of 9-11 minutes.
Do a quick release (carefully turn the steam valve to the venting position using the handle of a long spoon and wait for all of the steam to escape and the pin to drop down).
Remove lid, stir. You will see some liquid in the pot. This will absorb after just a few minutes. Wait for 3-5 minutes and then serve.