Wash and chop all of the veggies into big chunks and throw them into a pot. (You can use a pressure cooker or a slow cooker as well).
Fill the pot with enough water to cover the veggies by about ¼ inch. (About 5-6 cups, but go by how much you need to cover the veggies than the exact measurement).
Boil until all veggies are very soft. (If using a pressure cooker, just bring up to pressure and then turn off and wait until the pressure goes down). (If using a slow cooker, set to low for 8 hours or at high for 5 hours).
Add pesto (or basil and olive oil) and salt to the pot and puree with an immersion blender. (If you don't have an immersion blender transfer small amount to a blender to puree).
Serve hot with a dollop of additional pesto.
Notes
If using a crock pot, add an additional 1 cup of water.
If using an instant pot, set it to pressure cook for 1 minute, then allow the pressure to go down on its own.
Pro tips for delicious zucchini soup
I like to use a metal immersion blender for this soup. This way I don't have to transfer it to a blender and I'm not touching plastic to such hot liquid.
If you don't have an immersion blender, you can transfer small amounts to your blender to puree it, but be careful not to overfill the blender or hot liquid could leak out and burn you.
Pesto makes this soup delicious! It is hard to find dairy-free pesto in the stores, but super easy to make your own vegan pesto recipe.
Add slightly more water for a thinner soup, add less water, or an extra potato for a thicker soup.
If you are using a very large zucchini, be sure to cut out the section with large seeds.