Add the finely chopped mixed vegetables and mushrooms (if using). Stir-fry for a few minutes until they start to soften.
Pour in the soy sauce, vinegar, chili sauce, and tomato ketchup. Mix well to coat the vegetables.
Add the vegetable broth (or water) and bring the soup to a boil. Reduce the heat to a simmer and let the soup cook for about 10-15 minutes, allowing the flavors to meld.
Season the soup with black pepper and salt to taste.
Prepare the cornstarch slurry by mixing cornstarch and water. Gradually pour the slurry into the soup while stirring continuously. This will help thicken the soup slightly.
Increase the heat to medium and let the soup simmer for another 2-3 minutes, stirring occasionally, until it reaches your desired consistency.
Add the finely chopped spring onion greens and give it a final stir.
Have hot Man chow Vegetable Soup into serving bowls. Garnish with Steamed rice noodles. Add cilantro, and sliced green chilies.
Enjoy your flavorful and spicy Man chow Vegetable Soup!
Remember, you can adjust the spice levels, sauces, and vegetables according to your preference.