Heat olive oil in Instant Pot using sauté mode adjusted to high, until the oil starts to shimmer. Add the onions and chopped mushrooms to the pot and sprinkle with salt. Cook, stirring occasionally, until the mushrooms give up their liquid and start to brown, about 10 minutes.
Stir in the minced garlic and sauté 1 minute longer.
Pour in the arborio rice and stir the rice until it is coated with the olive oil and onions. Toast the rice for about 2 minutes, stirring frequently.
Add the dry white wine to the Instant Pot and let simmer for about 2 minutes, until the rice has absorbed the wine.
Stir in the lemon juice and vegetable broth. Turn off the sauté function and place lid on pressure cooker. Set the vent to sealed.
Cook at high pressure for 5 minutes. Quick release the pressure, then carefully remove the lid, tilting it away from you to avoid the scalding hot steam.
Stir butter into the rice until it melts, then stir in the grated cheese and lemon zest.
Serve, sprinkling with a little extra grated cheese and some minced parsley. Enjoy!