On saute mode add oil and chopped onion- allow onions to cook down for a few minutes.
Change mode to Slow Cook.
Add chopped zucchini, broth, lemon juice, lemon zest, red pepper flakes.
Stir and pop lid on and leave for 3 hours.
Let slow cook for 3 hours.
Turn off Instant Pot and mush with a potato masher.
Add pasta and water.
Turn mode to Pressure Cook and set for 1.5 minutes.
Once complete, turn off Instant Pot and release steam.
Sprinkle with nutritional yeast and serve