Pat both sides of the cod fillets thoroughly with a paper towel to remove excess moisture. Sprinkle evenly with kosher salt and set aside while preparing the broth components.

In a small bowl, combine 2 tablespoons of lime juice with the sliced Fresno chili. Allow the mixture to rest while preparing the remaining elements of the dish. The acidity of the lime juice will soften the chili and create a bright, tangy accompaniment for serving.

Set aside a paper towel–lined plate for draining the fried ginger.

In a Dutch oven or deep skillet over medium-high heat, add the canola oil. Once hot, add the minced ginger and sauté for 30 seconds to 1 minute, or until lightly golden. Remove the pan from heat immediately, as the ginger will continue to darken from residual heat.

Pour the ginger and oil mixture through a fine-mesh sieve into a heatproof bowl. Evenly spread the fried ginger onto the prepared plate to cool and crisp. Reserve the strained ginger-infused oil for later use.

Wipe the pan clean to remove any browned ginger residue. Return the reserved ginger oil to the pan and set the heat to medium-low. Add the minced garlic and sliced lemongrass, cooking for approximately 2 minutes or until aromatic and lightly golden.

Add the coconut milk, fish sauce, brown sugar, lime zest, and the remaining 1 tablespoon of lime juice to the pan. Stir to incorporate all ingredients thoroughly. Bring the mixture to a gentle boil over medium-high heat, then reduce the heat to medium. Allow the broth to simmer uncovered for 10 minutes to develop depth and balance in flavor. Taste and adjust seasoning with additional fish sauce, lime juice, or sugar as desired.

Lower the heat to a gentle simmer and add the bok choy. Cook for 1 to 2 minutes, or until the greens are wilted and the stalks have slightly softened while retaining some texture. Using a slotted spoon, transfer the bok choy to four serving bowls.

Carefully place the cod fillets into the simmering broth. Cover the pan and maintain a low heat, ensuring the liquid remains just below a boil. Cook the fish for approximately 6 to 9 minutes, depending on the thickness of the fillets, or until opaque and easily flakes with a fork. Thinner fillets may require less time. The internal temperature should reach between 140°F and 145°F (60°C to 63°C).

Gently remove the cooked cod using a slotted spatula and transfer each fillet to the bowls with the bok choy.

Return the pan to medium heat and simmer the remaining coconut lime broth for 3 to 5 minutes, allowing it to reduce slightly. The consistency should be velvety and able to coat the back of a spoon. Adjust the flavor balance one final time with additional lime juice or fish sauce as needed.

Divide the hot poaching liquid evenly among the bowls, covering the bok choy and cod. Garnish with crispy fried ginger, pickled chilies, lime wedges, and chopped cilantro. Serve immediately while hot, ensuring each bowl receives a balance of broth, fish, and garnish.