Start the pot: Set a large soup pot on the stove over medium-high heat. Add the neutral oil and let it warm for about 30 seconds.

Stir the mushrooms and cook for 2 to 3 minutes more, until they are browned in spots and most of their liquid has cooked away.

Add the sliced onion to the pot. Cook for 3 minutes, stirring now and then, until the onion softens and turns glossy.

Build the broth: Add the garlic, chopped ginger, and the white parts of the scallions to the pot. Stir for 1 minute, just until they smell fragrant.

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

Cook the noodles: Add the dried rice noodles to the boiling broth. Press them down with a spoon so they start to soften under the liquid.

Cook the noodles for 2 minutes, stirring gently once or twice to separate the strands.

Add the sliced bok choy stems to the pot. Cook for 2 minutes, keeping the broth at a gentle boil.

Add the torn bok choy leaves to the pot. Cook for 1 to 2 minutes more, until the leaves wilt and the noodles are tender but still hold their shape.

Finish the soup: Turn off the heat. Stir the juice from 1 lime into the soup.

Taste the broth. Add a little more soy sauce if you want a saltier, deeper flavor.

Serve: Ladle the soup into bowls, making sure each bowl gets noodles, mushrooms, and bok choy.