Mix miso, water, vinegar, sake, and sugar in a saucepan. Bring to a boil, whisk well. Remove from heat and allow to cool.
Add the cod and marinate for 24 hours.
Drain and bake at 400 for 10 minutes. Serve with red curry noodles.
Heat the oil, then sweat ginger, lemongrass, and garlic. Add curry paste and coconut milk and simmer. Whisk until smooth, then add fish sauce. Toss in noodles to warm, then toss with scallions and serve with cod.