Season the salmon fillets with salt and pepper on both sides.
Whisk together miso paste, soy sauce, brown sugar, rice vinegar, and sesame oil in a small bowl until smooth. Set aside 1 tablespoon of the mixture for glazing later.
Place the salmon in a dish and pour the miso mixture over the fillets. Cover and let marinate in the refrigerator for 1 to 3 hours.
Preheat your oven to 375°F. Place the marinated salmon fillets on a baking sheet lined with parchment paper and discard the leftover marinade.
Bake the salmon in the preheated oven for 12 to 15 minutes. The salmon should be nearly cooked through and opaque.
Brush the tops of the salmon fillets with the reserved tablespoon of miso glaze and broil on high for 1 to 2 minutes until caramelized.
Garnish with chopped green onions and sesame seeds before serving.