Step 1

Heat the oil in a large pot or Dutch oven over moderately high heat. Add the onion and garlic and cook until the onion is tender and translucent, 3-5 minutes. Add the tomatoes to the pot and cook until the tomatoes soften and release some of their liquid, 2 to 3 minutes. Pour in the white wine, stirring to scrape up any browned bits from the bottom of the pot. Increase the heat to high, and boil the wine until reduced by half, 3 to 5 minutes.

Step 2

Stir in the water, fish sauce, calamansi juice (or lemon juice, if using), and daikon. Bring everything to a boil, and then cover and simmer over low heat until the daikon is tender, 10 to 15 minutes.

Step 3

Ladle about a 1/2 cup of the liquid from the pot and into a small bowl. Add the miso to the bowl and whisk until the miso is completely dissolved. Pour the miso mixture into the pot and stir to combine.

Step 4

Season the salmon with the black pepper, and then add the salmon and the mustard greens (or bok choy, if using) to the pot and gently simmer until the salmon is just cooked through and the greens are wilted, 2 to 3 minutes. Remove the pot from the heat.

Step 5

Taste the soup and add more calamansi juice (or lemon juice, if using) if more sourness is desired, or add more miso if a more savory flavor is desired.

Step 6

Serve immediately with steamed white rice on the side.