Spray a cooking pan with non-stick cooking spray and set aside.
Add the ingredients for the miso ginger marinade/sauce in a food processor.
Mix/pulse ingredients for a few minutes until everything is finely blended.
After the ingredients are blended, put half of the marinade in a separate container, we will use this a bit later in the process. Apply the other half of the marinade to each fillet, thoroughly coating each fillet.
Place salmon fillets in a covered dish and then in the refrigerator for 30 - 45 minutes.
Remove dish from refrigerator and scrape off excess miso ginger sauce.
Turn broiler on high. Place the fillets in a cooking pan that you've sprayed with your nonstick cooking spray. Place pan on the top rack of the oven on broil (hi) for 4 - 5 minutes.
About halfway through the broiling process, remove the cooking pan from the oven. Get the other half of the sauce you mixed up earlier and apply a good coating of the sauce to your fillets. Return your fillets to the oven to finish cooking.
After the second half of your cooking time expires (4 - 5 minutes cook time total), remove the fillets from the oven. Using a fork, test how easily the salmon flakes apart. Salmon that is properly cooked should have an internal temp of 145 F and flake easily. Thicker fillets may require a few more minutes under the broiler.
Top with the chopped green onions. Enjoy!
Notes
Because the salmon is cooked under the broiler, I recommend using avocado oil for its high smoke point while keeping the toasted sesame oil for its rich, nutty flavor.
Don't marinate the salmon for longer than 45 minutes. The miso and soy sauce can make the fish overly salty and affect its texture if left too long.
Choosing fillets that are about the same thickness helps them cook evenly under the broiler.
Pureeing the apple with the miso, ginger, mirin, soy sauce, and sesame oil creates a smooth marinade that coats the salmon beautifully.
The apple and mirin help the topping caramelize beautifully, so keep a close eye on the salmon during the last few minutes under the broiler.
Cooking time will vary depending on the thickness of your salmon fillets. For the juiciest salmon, check the internal temperature with an instant-read thermometer instead of relying on time alone.
Position the salmon about 6 inches below the broiler. This gives the salmon enough time to cook through while the topping lightly caramelizes without burning.