In a medium bowl, add the miso, mirin, honey, garlic powder, and avocado oil. Whisk well to combine.
Add the cod and coat both sides of the fish in the miso sauce. Cover and marinate in the fridge for 24 hours. This can be marinated for 36 hours if needed or at least 1 hour if you don't have much time.
Preheat oven to 400
On a baking sheet lined with parchment paper, add the cod and roast in the oven for about 10-12 minutes.
Serve with your favorite sides like rice and bok choy and top with scallions and sesame seeds.
Enjoy!