In a large pot, over medium heat on the stove, sauté onion and garlic for 5-7 minutes. Use splashes of water to keep them from sticking.
Add zucchini and sauté for another 3 minutes.
Then add veggie broth, garlic powder, oregano and nutritional yeast to the pot. Stir everything together.
Bring to a boil. Cover the pot with a lid and bring to a simmer for 20 minutes.
When the soup is done simmering, stir in the avocado and basil leaves.
If you have an immersion blender, use that to blend the soup. If using a regular blender, let the soup cool down for a few minutes, before pouring it in the blender. Blend until it's smooth and creamy.
Taste soup incase you want to adjust some of the seasonings. Return to pot, reheat if needed and serve.