Place the stainless steel inner pot inside the Instant Pot®. Press Saute and set the time to 10 Minutes. Add olive oil; when hot, add the onion and cook, stirring, until soft and starting to brown. When done, press Cancel.
Add the zucchini, zest, garlic, vegetable broth and seasoning. Stir well so that no onions remain stuck to the bottom.
Press Cancel, close and lock the Instant Pot® lid. Make sure the steam release handle is turned to Sealing. Press Pressure Cook, pressure level High, and set the time to 3 Minutes.
When done, press Cancel and turn the steam release handle to Venting. Once all the pressure is released, open the lid, add the spinach leaves and stir until soft. Blend the soup until uniform. Add cream along with the lemon juice, and serve. Garnish with cream, croutons and chives.