Prep aromatics: peel ginger and turmeric and cut into chunks, smash and peel garlic, and cut off chili stems so seeds are exposed
Combine all ingredients besides the cod in a sauce pan and simmer on low covered until flavor has infused into broth. The turmeric should turn it yellow. Taste and adjust for salt - depending on saltiness of fish sauce it may need about 1/2-1 tsp salt. It may need none.
Dry cod and salt on both sides
Turn heat up on coconut milk broth to medium, then submerge cod as much as possible. If they don't fully submerge, it's ok. Just stir and baste so some of the broth gets on the top of the fish.
Cover and poach for 6-8 minutes, until flaky.
Serve with fresh lime juice, rice, and vegetable of choice.