Prep the vegetables: Start by finely chopping the onion, green bell pepper, scallions, celery, red cabbage, and green beans. Mince the garlic and grate the ginger. Have all your ingredients ready to go.
Heat the oil: In a large pot, heat 1 tablespoon of sesame oil over medium heat.
Cook the aromatics: Add the finely chopped onion to the pot and sauté for 2-3 minutes until softened. Next, stir in the garlic, ginger, and celery. Cook for another 1-2 minutes until fragrant.
Add vegetables: Stir in the chopped bell pepper, green beans, and red cabbage. Let the vegetables sauté for about 5 minutes, stirring frequently. You want them to soften but still retain some crunch.
Stir in the soy sauce, and season with salt and pepper to taste.
Add the broth: Pour in 4 cups (1 liter) of chicken broth. If you prefer a vegetarian version, you can substitute the chicken broth with vegetable broth.
Simmer the soup: Allow the soup to come to a boil, then reduce the heat to low and let it simmer for about 10 minutes. This will allow the flavors to meld together without overcooking the vegetables.
Prepare the noodles: While the soup is simmering, cook a small portion of rice noodles (about 1/2 cup or 50 g). Drain the noodles and set them aside.
Final touches: After the soup has simmered, stir in the cooked rice noodles. Give everything a good mix and taste the soup to adjust any seasonings if necessary.
Serve: Ladle the soup into bowls and garnish with a sprinkle of chopped green onions. Serve hot and enjoy!