Add onion and cook until softened, about 3 minutes. Add garlic and cook for 1 minute more until fragrant.
Pour in marinara sauce, beef broth, diced tomatoes, oregano, basil, and red pepper flakes. Stir well to combine, scraping up any browned bits from the bottom of the pot.
Add the broken lasagna noodles. Do not stir after adding noodles.
Secure the lid and set the vent to Sealing. Cook on Manual/Pressure Cook High for 4 minutes.
When the cooking time is complete, perform a Quick Release of the pressure.
Stir in heavy cream, water, spinach, and Parmesan cheese. Let the soup sit for 5 minutes to allow the spinach to wilt and the soup to thicken slightly.
Taste and adjust seasoning with salt and pepper. Serve hot with extra Parmesan cheese.
Notes
If you prefer a less creamy soup, reduce the heavy cream to 1/4 cup.
You can substitute ground turkey or Italian sausage for the ground beef.