Bring a kettle or medium saucepan of water to a boil for the noodles.

Put the rice noodles in a large heatproof bowl.

Pour the boiling water over the noodles. Let them soak for 6 to 8 minutes, stirring once, until they bend easily but still feel a little firm in the center.

Drain the noodles in a colander and rinse them under cold water. Set them aside so they do not keep cooking.

Set a large soup pot over medium-high heat and add the oil.

Put the tofu cubes into the pot in a single layer. Cook for 4 to 5 minutes, turning once or twice, until they are lightly browned on several sides.

Transfer the tofu to a plate.

Add the scallion whites, red bell pepper, and garlic to the same pot. Cook for 2 to 3 minutes, stirring often, until the pepper starts to soften and the garlic smells fragrant.

Add the black bean garlic sauce to the pot. Stir for 30 seconds so it coats the vegetables.

Pour the vegetable broth into the pot. Stir and scrape the bottom of the pot with a wooden spoon to loosen any browned bits.

Stir the soy sauce into the broth and raise the heat until the pot comes to a gentle boil.

Add the napa cabbage to the pot. Cook for 3 to 4 minutes, stirring once or twice, until the cabbage is wilted and just tender.