Add oil and onion. Let cook 4 minutes or until onion is soft.
Add garlic and cook an additional 30 seconds until fragrant.
Remove garlic and onion and spread in the bottom of a (7") cake pan.
Clean inner pot and place back inside Instant Pot®. Add water and trivet to pot.
Arrange sliced vegetables in a pattern of squash, zucchini, tomato, potato around the edge of the cake pan. Continue in the center of the pan until the vegetables are all used.
Top with a paper towel and cover top of pan tightly with foil. Create a foil sling and carefully lower cake pan into Instant Pot®.
Close lid and set pressure release to Sealing.
Press Manual or Pressure Cook button and adjust time to 30 minutes.
When the timer beeps, allow pressure to release naturally for 10 minutes. Quick release remaining pressure and then unlock lid and remove it.
Remove pan from Instant Pot® using foil sling. Sprinkle salt, pepper, mozzarella, and Parmesan cheese on top. Serve warm.