Saute the onion until its transparent. Peel avocado and remove the pit. Combine the onion, avocado, soy sauce and water in a food processor or blender and beat well. When the mixture is smooth put into a saucepan and let it come to a boil. Simmer for 2 or 3 minutes. Serve right away or it will discolor. This is a very creamy unusual soup.