Pre-heat oven to 425 degrees.
While oven heats, place salmon fillets on a foil-lined cooking sheet. Pat fillets with paper towel to remove excess moisture. Coat top of each fillet with 1 tsp olive oil and use fingers to evenly distribute oil over salmon.
Once oven is preheated, cover fillets with foil and bake 13-15 minutes.
While the oven preheats and salmon bakes, prepare sauce.
Peel fresh ginger root with the edge of a teaspoon.
Grate ginger using microplane or grater and set aside.
Peel and finely chop garlic cloves and set aside.
Finely chop 2-3 green onion and set aside.
Mix Shoyu and Aji-Mirin in a mixing bowl. If more sauce is needed, increase amount but keep ratio.
Add garlic and ginger to the sauce mixture and stir and set aside.
Heat sesame oil in a large saucepan on stovetop until it starts to slightly smoke. Do not overheat, as it will burn.
Turn off heat and carefully add the shoyu, aji-mirin, garlic, ginger mixture to the hot sesame oil pan. It will splatter, so please be careful. Using an oversized saucepan with high sides will reduce the potential for spattering on stovetop.
Stir until ingredients are well mixed.
One salmon fillets are thoroughly cooked and plated, add sauce to the top of each fillet.
Sprinkle the salmon fillets with chopped green onion to taste.