Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper.
In a small bowl, mix together the miso paste, softened butter, honey, soy sauce, and sesame oil until well combined.
Pat the salmon fillets dry with paper towels and season both sides with salt and pepper.
Place the salmon fillets skin-side down on the prepared baking sheet. Spread the miso butter mixture evenly over the top of each fillet.
Bake the salmon in the preheated oven for 12-15 minutes, or until the salmon is cooked through and flakes easily with a fork.
While the salmon is baking, heat the vegetable oil in a small skillet over medium heat. Add the chopped scallions and sauté for about 2-3 minutes until they are tender and slightly crispy.
Remove the salmon from the oven and let it rest for a couple of minutes. Top with the sautéed scallions and sprinkle with sesame seeds if using.