In large bowl, whisk together the corn starch, cooking wine, spring onion, ginger, salt and pepper, and egg white. Add the fish slices and marinate for 1 hour.
When the fish is ready, peel the tomatoes and dice. In a large pot on medium heat 2 tablespoons of oil and add the spring onion and garlic until aromatic, add the diced tomatoes and reduce the heat to low and cook for about 7 to 10 minutes until the tomatoes are soft and lots of juice is released. Add 8 cups of hot water and simmer for 20 minutes.
Add the celery, red onion, and mushrooms and cook for another 10 minutes, season with salt and pepper to taste.
Turn up the heat to medium and add the fish slices and marinade and stir, cook for about 30 seconds to 1 minute or until the fish slices turn white, remove from heat and carefully pour into a large serving bowl.
Optional, heat 2 tablespoons of oil in a small pan or wok until slightly smoking and pour into the soup.
Sprinkle coriander and and spring onion on the top and serve.