Add avocado oil (or extra virgin olive oil, butter or ghee) to a large stock pot over medium heat. Once heated through, add the onion, garlic and celery, and stir. Cook, stirring occasionally for a few minutes.
Next, add the zucchini and potatoes, and stir. Season to taste with sea salt and black pepper. Continue to cook, stirring occasionally, for 5-7 minutes. Then, add the broth and bring to a boil. Reduce heat to a simmer and cover partially with a lid (keep it ajar a little bit). Simmer for 20 minutes.
Remove from heat and add to a high-powered blender container (may need to do in two batches depending on your blender). Blend until smooth. Return blended soup to pot and taste. Add more sea salt and/or black pepper, if desired.
If desired, serve with fresh herbs of choice and/or raw grated zucchini. Store any leftovers in a covered container in the fridge and eat within 2-3 days.