Start by washing the zucchini and spinach thoroughly. For the zucchini, chop off the ends and dice them into medium-sized chunks.
Peel and finely chop the onion. Set it aside.
In a large pot, heat the olive oil over medium heat. Once hot, add the onions. Sauté them for about 3-4 minutes or until they become translucent.
Add the minced garlic to the pot and continue to sauté for another 1-2 minutes.
Introduce the chopped zucchini to the pot. Cook for about 5-7 minutes, ensuring the zucchini starts to soften.
Pour in the vegetable broth. Increase the heat to bring the mixture to a boil.
Once boiling, reduce the heat to a simmer. Allow the Vegan Zucchini and Spinach Soup to cook for about 10 minutes.
Add the fresh spinach leaves, ensuring they are submerged in the soup.
Continue to simmer for another 3-5 minutes until the spinach wilts.
Season with salt, black pepper, and if using, the nutritional yeast.
Remove from heat and blend the soup using an immersion blender until smooth or transfer to a blender in batches. Be cautious when blending hot liquids!
Once smoothly blended, stir in the lemon juice. Taste and adjust seasonings if necessary.