Set the Instant Pot to the 'Sauté' function on high. Add the olive oil. Once hot, add the ground beef and diced onion. Cook, breaking up the beef with a spoon, until the beef is browned and the onion is soft, about 5-7 minutes. Drain any excess grease from the pot.
Stir in the minced garlic, Italian seasoning, salt, pepper, and optional red pepper flakes. Cook for another minute until the garlic is fragrant.
Press 'Cancel' to turn off the Sauté function. Pour in about 1/2 cup of the beef broth and use your spoon to scrape any browned bits from the bottom of the pot. This is crucial to prevent a 'BURN' warning.
Pour in the remaining beef broth, followed by the entire jar of marinara sauce. Do NOT stir.
Spread the uncooked ziti evenly on top of the sauce. Use the back of your spoon to gently press the pasta down until it is mostly submerged in the liquid. Again, do not stir everything together.
Secure the lid on the Instant Pot and set the steam release valve to the 'Sealing' position. Select 'Pressure Cook' (or 'Manual') and set the timer for 5 minutes on high pressure.
Once the cooking time is complete, perform a quick release by carefully moving the steam release valve to the 'Venting' position. Be cautious of the hot steam.
Once the pin has dropped, carefully open the lid. Give the pasta a good stir to combine everything. It may look a little watery at first, but it will thicken. Stir in the Parmesan cheese and 1 cup of the shredded mozzarella until melted and creamy.
Sprinkle the remaining 1 cup of mozzarella cheese over the top of the ziti. Place the lid back on the Instant Pot for 2-3 minutes (with the power off) to allow the cheese to melt into a gooey layer.
Garnish with fresh parsley and serve immediately.
Notes
Burn Notice Prevention: The two most important steps to prevent the 'BURN' notice are to thoroughly deglaze the pot after sautéing and to layer the ingredients without stirring before pressure cooking.Pasta Choice: Penne pasta can be used as a substitute for ziti with the same cooking time.Storage: Leftovers can be stored in an airtight container in the refrigerator for up to 4 days.Variations: Feel free to substitute the ground beef with ground Italian sausage (mild or hot) or ground turkey.
Keyword ground beef pasta, Instant Pot Ziti, One Pot Dinner