Start by setting your Instant Pot to the sauté function. Add the olive oil and let it heat up. Once hot, add the finely minced onion and garlic. Sauté for about 2-3 minutes until they are softened and fragrant.
In a mixing bowl, combine the ground beef, Italian bread crumbs, Parmesan cheese, salt, pepper, and minced onion. Mix until just combined. Be careful not to overwork the meat. Form the mixture into small meatballs, about 1 inch in diameter.
With the sauté function still active, add the meatballs to the pot. Brown them on all sides for about 5 minutes. Once browned, remove the meatballs and set them aside.
Pour in the low-sodium beef broth, pasta sauce, and diced tomatoes into the pot, scraping the bottom to deglaze any browned bits.
Break the spaghetti into thirds and add it to the sauce mixture. Gently push the pasta down into the liquid. Do not stir.
Carefully place the browned meatballs on top of the spaghetti.
Close the lid of the Instant Pot, ensuring the valve is set to sealing. Set the Instant Pot to high pressure for 8 minutes. Once the cooking time is up, allow for a natural pressure release for about 5-10 minutes before performing a quick release.
Once the pressure is released, open the lid and give the spaghetti and meatballs a gentle stir to combine. Serve hot, garnished with extra Parmesan cheese if desired.
