Set a large soup pot on the stove over medium heat.

Add the neutral oil to the pot and let it heat for about 30 seconds, until it looks loose and shiny.

Add the scallion whites to the pot. Cook for 1 minute, stirring, until they soften.

Start the broth: Add the kimchi and the kimchi brine to the pot. Cook for 2 minutes, stirring often, until the kimchi looks glossy and smells less sharp.

Add the sliced shiitake mushrooms to the pot. Cook for 3 to 4 minutes, stirring every so often, until the mushrooms shrink and start to soften.

Stir the soy sauce into the mushroom and kimchi mixture.

Bring the soup together: Pour the vegetable broth into the pot. Raise the heat to high.

Bring the broth to a full boil.

Add the sliced zucchini to the boiling broth. Lower the heat to medium and let it simmer for 3 minutes, until the zucchini is just tender.

Add the dried rice noodles to the pot. Press them down into the broth so they are mostly covered.

Cook the noodles for 3 to 5 minutes, or according to the package directions, stirring once or twice so they do not stick together. They should be tender but still hold their shape.

Add the baby spinach to the pot. Stir for 1 minute, until the spinach wilts into the broth.