Preheat oven to 425°F. Line a baking sheet with parchment paper. Pat salmon fillets completely dry with paper towels and place on prepared baking sheet.

In a small bowl, whisk together miso paste, maple syrup, rice vinegar, mirin (if using), minced garlic, grated ginger, and sesame oil until smooth. Reserve 2 tablespoons of glaze for serving.

Brush salmon fillets generously with about two-thirds of the miso glaze. Let sit at room temperature for 10 minutes to allow flavors to penetrate.

Bake salmon for 8 minutes, then remove and brush with remaining glaze. Return to oven and bake for 4-7 minutes more, until salmon flakes easily and internal temperature reaches 145°F.

Remove from oven and let rest for 2 minutes. Drizzle with reserved glaze, sprinkle with chopped scallions and sesame seeds. Serve immediately.