Set a large pot or Dutch oven on the stove over medium-high heat.

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

Add the sliced mushrooms to the pot in an even layer. Cook them for 5 to 6 minutes, stirring a few times, until they shrink, give off their liquid, and start to brown around the edges.

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

Add the sliced garlic and grated ginger to the pot. Cook for 30 seconds, stirring, until fragrant.

Add the doenjang to the pot. Stir it through the vegetables for about 30 seconds so it starts to loosen and coat the mushrooms.

Pour the vegetable broth into the pot. Stir well and press the doenjang against the side of the pot with your spoon so it dissolves into the broth.

Stir the soy sauce into the pot. Raise the heat to high and bring the broth to a boil.

Add the sliced zucchini to the boiling broth. Cook for 2 minutes, until it just starts to soften.

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

Cook the noodles for 4 to 5 minutes over a steady boil, stirring often, until the noodles are tender and easy to separate with a spoon or tongs.

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