Soften the noodles: Fill a kettle or saucepan with water and bring it to a boil.

Put the rice noodles in a large heatproof bowl.

Pour the boiling water over the rice noodles. Let them soak for 6 to 8 minutes, until they are flexible but still a little firm in the center.

Drain the noodles in a colander. Rinse them briefly under cool water so they stop softening, then set them aside.

Start the broth: Set a large soup pot over medium heat and add the oil.

Put the scallion whites and the garlic into the pot. Cook for 1 to 2 minutes, stirring often, until the scallions look softened and the garlic smells fragrant.

Add the halved tomatoes to the pot. Cook for 3 to 4 minutes, stirring once or twice, until the tomatoes slump and some of them split open.

Stir the tamarind concentrate, tamari, and sugar into the pot. Cook for 30 seconds so the tamarind loosens and mixes into the vegetables.

Pour the vegetable broth and the reserved 2 tablespoons pineapple juice into the pot. Raise the heat to medium-high and bring the broth to a gentle boil.

Add the sliced okra to the pot. Simmer for 4 minutes, until the okra is tender and the broth looks slightly thicker.

Put the pineapple chunks into the pot. Simmer for 1 minute, just until they are heated through.

Taste the broth. Stir in the kosher salt, and add a little more if the broth still tastes flat.