Season cod with salt and pepper on both sides.
Heat oil in pan on medium high heat.
Saute chilli, garlic, and shallot for 1 minute.
Add lemongrass and galangal, saute for another minute.
Pour in coconut milk, lime leaves, basil leaves, cilantro roots, and fish sauce.
Add cod to pan. Fish doesn't need to be fully submerged.
Bring coconut milk to boil, lower heat to a gentle simmer.
Cover and cook for about 5 minutes.
Remove cod from coconut broth, and add nai bai.
Cover and allow to cook until vegetable is wilted. About a minute.
Remove from heat and stir in lime juice.
Spoon nai bai and broth over fish, and garnish with cilantro leaves.