Mix miso, mirin, sake, sugar, and soy sauce in a bowl.
Add sesame oil, ginger, and garlic. Stir well.
Put salmon in a dish and cover with the sauce.
Wrap with plastic and keep in the fridge for 12-24 hours.
Heat the oven to 400°F (200°C). Put parchment on a baking sheet.
Take the salmon out of the sauce. Let extra sauce drip off.
Put salmon on the baking sheet, skin down.
Brush lightly with vegetable oil.
Bake for 10-12 minutes. Then, broil for 2-3 minutes to brown the top.
Sprinkle scallions on top and serve hot.