Preheat oven to 400F. Line a baking sheet with parchment paper and place salmon fillets on top.
Add mirin to a small saucepan over medium-high heat. Bring the mirin to a boil, and allow to boil for about 1 minute.
Then, reduce the heat and add minced garlic. Stir around for about 30 seconds, then add miso paste. Whisk until the miso paste starts to dissolve and break down.
Then, add the grated ginger, rice vinegar, maple syrup, and avocado oil. Bring everything to a boil again, whisking continuously for 1 minute.
Once a smooth sauce has formed, turn off the heat. Spoon 1/2 of the sauce over top of the salmon fillets, coating evenly.
Place salmon in the oven for 12-15 minutes, depending on thickness and desired doneness.
When salmon is cooked, remove from oven. Serve with desired sides (ideas included in notes below!) and finish with the remainder of sauce and some black pepper. Enjoy hot!