Set Instant Pot to "saute." Add olive oil, optional chopped onions and optional minced garlic. Allow to cook until tender and slightly translucent.
Add ground beef, salt, onion powder and garlic powder, breaking up the beef and stirring until it is no longer pink.
Turn Instant Pot Off.
Pour 1/2 cup of water and all of the pasta/marinara sauce into the pot. Stir to combine well, making sure to scrape any stuck-on bits from the bottom.
Place broken spaghetti on top, half going north and south, half east and west in a criss-cross pattern.
Pour remaining 1 ½ cups water over the top of the spaghetti. Do. Not. Stir!
Apply Instant Pot lid, setting the pressure valve to "Seal."
Set Instant Pot to High Pressure for 8 minutes. It will take 10 to 12 minutes to come to pressure.
Open the pressure lease valve (quick release) as soon as the 8 minutes cook time is complete.
Open the pressure cooker and gently stir the spaghetti into the sauce. Look at that!
Serve immediately with grated Parmesan cheese, as desired.