Except for the mix-ins/toppings, add all of the ingredients and 1 cup of the water to a powerful blender or a food processor fitted with the blade attachment. Blend until the mixture is very smooth. Taste, and only if necessary, season with a bit more salt and pepper.
Add the water, ½ to 1 cup at a time, to the desired consistency.
For the mix-ins
Combine the avocado, tomato and onion and mix-in all but about ½ cup to the soup. When you serve the soup, add the remaining mix-ins on top of each serving for garnish.
Assembly
Drizzle a little extra virgin olive oil on top and sprinkle with a bit of coarse sea salt.