Preheat your oven to 375 °F then switch to broil. (only if cooking in the oven, see full instructions below)
In a bowl, whisk together the miso paste, soy sauce, brown sugar, sesame oil and garlic. Taste, adjust any ingredient to suit your taste and set aside.
Place a skillet or nonstick pan over a high heat. Add the olive oil and then add the fish, top side down. Sear for 2-3 minute and then turn the fish over.
Brush the top of the cod generously with the miso glaze and then transfer the pan to the oven. ( if your pan is not oven safe, transfer the fish to a parchment paper lined baking sheet. Roast for 6-8 minutes brushing with more glaze if desired.
Take the fish from the oven and check for doneness. The fish should feel firm when pressed and flake easily with a fork.
We enjoyed it with some veg loaded fried rice