Push sauté mode button on Instant Pot. Wait until pot reads HOT on screen and then add oil, sausage and onion. Brown the meat and cook onions until translucent. Add garlic towards the end of cooking, to prevent burning.
Add 1 cup of water into Instant Pot and deglaze the pan by scraping the cooked bits of food off the bottom with a spatula.
Add remaining 3 cups of water, tomato sauce, noodles and seasonings and stir.
Push cancel to stop saute mode. Place lid on Instant Pot and turn venting knob to sealing position. Cook on manual high pressure for 10 minutes. Quick release the pressure.
Serve with mozzarella or ricotta cheese on top of soup with a side of breadsticks.
(For gluten free option, we prefer using the Tinkyada brand noodles and cooking the soup for 8 minutes on high pressure, followed by a quick pressure release.)