Start by preheating your oven to 400°F (200°C). In a small bowl, mash together the white miso paste and softened butter using a fork. Mix until the texture becomes smooth and evenly combined.
Place the salmon fillets on a baking sheet with the skin side facing down. Spread the miso butter mixture evenly across the top of each piece. Finish by seasoning lightly with black pepper for extra flavor.
Transfer the tray to the oven and bake the salmon for about 15 minutes. The fish should become tender and flaky while the miso butter melts and forms a flavorful glaze.
While the salmon is cooking, add the chopped scallions, sliced shallot, minced garlic, and crushed red pepper to a medium bowl. This mixture forms the aromatic base of the salsa.
Heat olive oil in a small pan over medium heat until hot but not smoking. Carefully pour the hot oil over the scallion mixture in the bowl. The ingredients will sizzle slightly, releasing their aroma and flavor.
Let the mixture sit for about 10 minutes so the flavors blend together. After that, stir in the chopped cilantro, red wine vinegar, and fresh lemon juice.
Once the salmon is done baking, place it on a plate or over a bowl of rice or greens. Spoon the sizzled scallion salsa verde generously over the top and serve immediately.