Prep and cook instructions are almost identical for all fish options.

• Scrub or peel the potatoes; cut the potatoes in half lengthwise. Cut each half lengthwise into 1-inch-thick slices, then crosswise into 1-inch cubes.
• Cut the cod or halibut into 1-inch pieces, the trout into 2-inch pieces; season the fish lightly with salt and pepper.

In a large sauce pot over medium-high heat, warm 1 to 2 tablespoons oil until hot but not smoking. Add the potatoes and mirepoix, season with salt and pepper, and cook, stirring occasionally, until the vegetables start to soften, 3 to 4 minutes. Stir in the tomatillos, 2 cups [3 cups] water, and either ¼ cup [½ cup] white wine (from your pantry) or additional water and bring to a boil, scraping up any browned bits from the bottom of the pot. Reduce to a simmer, add the fish, cover, and cook until the vegetables are tender and the fish is opaque and flaky, 3 to 5 minutes.
While the fish simmers, prepare the lemon.

• Cut the lemon into wedges for garnish.

To the pot with the chowder, working in batches if needed, stir in the chard and cook until just wilted, 1 to 2 minutes. Remove from the heat and stir in the parsley puree and half the fish sauce. Season to taste with salt, pepper, and more fish sauce.

Transfer the chowder to individual bowls and serve with the lemon wedges.